diff --git a/S2OJ/1800/1800.cpp b/S2OJ/1800/1800.cpp
new file mode 100644
index 00000000..d924ba88
--- /dev/null
+++ b/S2OJ/1800/1800.cpp
@@ -0,0 +1,155 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5;
+
+int cnt, tot, root[N], lst[N], tr[N << 5][2], siz[N << 5];
+
+void insert(int val) {
+    root[++tot] = ++cnt;
+
+    int l = root[tot - 1], r = root[tot];
+
+    for (int i = 30; i >= 0; i--) {
+        bool x = val >> i & 1;
+
+        tr[r][x ^ 1] = tr[l][x ^ 1];
+        tr[r][x] = ++cnt;
+
+        l = tr[l][x];
+        r = tr[r][x];
+
+        siz[r] = siz[l] + 1;
+    }
+
+    lst[tot] = cnt;
+}
+
+int query_max_xor(int l, int r, int val) {
+    int res = 0;
+
+    l = root[l], r = root[r];
+
+    for (int i = 30; i >= 0; i--) {
+        bool x = val >> i & 1,
+             v = siz[tr[r][x ^ 1]] > siz[tr[l][x ^ 1]] ? (x ^ 1) : x;
+
+        l = tr[l][v];
+        r = tr[r][v];
+        res |= v << i;
+    }
+
+    return res;
+}
+
+int query_leq_cnt(int l, int r, int val) {
+    int res = 0;
+
+    l = root[l], r = root[r];
+
+    for (int i = 30; i >= 0; i--) {
+        bool x = val >> i & 1;
+
+        if (x) res += siz[tr[r][0]] - siz[tr[l][0]];
+
+        l = tr[l][x];
+        r = tr[r][x];
+    }
+
+    res += siz[r] - siz[l];
+
+    return res;
+}
+
+int query_kth(int l, int r, int k) {
+    int res = 0;
+
+    l = root[l], r = root[r];
+
+    for (int i = 30; i >= 0; i--) {
+        if (siz[tr[r][0]] - siz[tr[l][0]] >= k) {
+            l = tr[l][0];
+            r = tr[r][0];
+        } else {
+            res += 1 << i;
+            k -= siz[tr[r][0]] - siz[tr[l][0]];
+
+            l = tr[l][1];
+            r = tr[r][1];
+        }
+    }
+
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int q;
+
+    cin >> q;
+
+    while (q--) {
+        int op;
+
+        cin >> op;
+
+        switch (op) {
+            case 0: {
+                int x;
+
+                cin >> x;
+
+                insert(x);
+
+                break;
+            }
+
+            case 1: {
+                int l, r, x;
+
+                cin >> l >> r >> x;
+
+                cout << query_max_xor(l - 1, r, x) << endl;
+
+                break;
+            }
+
+            case 2: {
+                int k;
+
+                cin >> k;
+
+                cnt = lst[tot -= k];
+
+                break;
+            }
+
+            case 3: {
+                int l, r, x;
+
+                cin >> l >> r >> x;
+
+                cout << query_leq_cnt(l - 1, r, x) << endl;
+
+                break;
+            }
+
+            case 4: {
+                int l, r, k;
+
+                cin >> l >> r >> k;
+
+                cout << query_kth(l - 1, r, k) << endl;
+
+                break;
+            }
+        }
+    }
+
+    return 0;
+}
diff --git a/S2OJ/1800/data/operator1.ans b/S2OJ/1800/data/operator1.ans
new file mode 100644
index 00000000..15fddbff
--- /dev/null
+++ b/S2OJ/1800/data/operator1.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6738a5c7814f1c2941d9b102babc25a4e1961cab6723ffb0ce0bd17b191eccc0
+size 12147
diff --git a/S2OJ/1800/data/operator1.in b/S2OJ/1800/data/operator1.in
new file mode 100644
index 00000000..bad7df63
--- /dev/null
+++ b/S2OJ/1800/data/operator1.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:d233bdf691075cd54120c729582397e51aae0753a5366790d1bbd9f9b1c11210
+size 53797
diff --git a/S2OJ/1800/data/operator10.ans b/S2OJ/1800/data/operator10.ans
new file mode 100644
index 00000000..33ee0675
--- /dev/null
+++ b/S2OJ/1800/data/operator10.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:dbb00b492ed6eb65ac3f402e67a8426e18d119435e2e18a6f537ef06d11f1618
+size 1888628
diff --git a/S2OJ/1800/data/operator10.in b/S2OJ/1800/data/operator10.in
new file mode 100644
index 00000000..5e1ea65b
--- /dev/null
+++ b/S2OJ/1800/data/operator10.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:44121d22db30d8c333b04b8b63b72f1be34483cca21b99eb166a23a309afabcd
+size 7794464
diff --git a/S2OJ/1800/data/operator2.ans b/S2OJ/1800/data/operator2.ans
new file mode 100644
index 00000000..f5fa7424
--- /dev/null
+++ b/S2OJ/1800/data/operator2.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b76dcab92c88232efbaa22ae97d29089a95b62d1912af397f19cf0faf5e1c35a
+size 11860
diff --git a/S2OJ/1800/data/operator2.in b/S2OJ/1800/data/operator2.in
new file mode 100644
index 00000000..9960c120
--- /dev/null
+++ b/S2OJ/1800/data/operator2.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9b1f9b15ce0f448683a947d9ce239ed9fc732b1f19298a4aabc3b961073b05fd
+size 53168
diff --git a/S2OJ/1800/data/operator3.ans b/S2OJ/1800/data/operator3.ans
new file mode 100644
index 00000000..91df0aba
--- /dev/null
+++ b/S2OJ/1800/data/operator3.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2904326a06fd93238286be8875645a99fa8dcf0b676b81ae1176fa461a35fa69
+size 267952
diff --git a/S2OJ/1800/data/operator3.in b/S2OJ/1800/data/operator3.in
new file mode 100644
index 00000000..d8c10fc7
--- /dev/null
+++ b/S2OJ/1800/data/operator3.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9c7857d4e5cf458d8532d8c28ce1af6a8b0ec226668bba50fe78365974c31a50
+size 1342470
diff --git a/S2OJ/1800/data/operator4.ans b/S2OJ/1800/data/operator4.ans
new file mode 100644
index 00000000..57786504
--- /dev/null
+++ b/S2OJ/1800/data/operator4.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:79dfcbf213e071b34b843305dd168893238408b4019ac79221649f06ed2a5a6d
+size 244263
diff --git a/S2OJ/1800/data/operator4.in b/S2OJ/1800/data/operator4.in
new file mode 100644
index 00000000..62f58b6d
--- /dev/null
+++ b/S2OJ/1800/data/operator4.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:31e440c6c7f882f48bca1169f68e2fb34f98b217e3694101221a8c3d3c462c3b
+size 1303974
diff --git a/S2OJ/1800/data/operator5.ans b/S2OJ/1800/data/operator5.ans
new file mode 100644
index 00000000..00d11514
--- /dev/null
+++ b/S2OJ/1800/data/operator5.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:16a323123e3b47849d2473c03d3797d1e8b034735e0a9c9ae7c2a26170005b8a
+size 497625
diff --git a/S2OJ/1800/data/operator5.in b/S2OJ/1800/data/operator5.in
new file mode 100644
index 00000000..7e960ec8
--- /dev/null
+++ b/S2OJ/1800/data/operator5.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:3f996011354c8ab0506ece3e9f699ffa6f31734ca82cf4fde3b90e09c6cb9a6b
+size 2589509
diff --git a/S2OJ/1800/data/operator6.ans b/S2OJ/1800/data/operator6.ans
new file mode 100644
index 00000000..0306a613
--- /dev/null
+++ b/S2OJ/1800/data/operator6.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:356e5ac1bba140b061074a35cdfe2ea8de7299262becb13a5884ae6fc42c1067
+size 560069
diff --git a/S2OJ/1800/data/operator6.in b/S2OJ/1800/data/operator6.in
new file mode 100644
index 00000000..2156c7ee
--- /dev/null
+++ b/S2OJ/1800/data/operator6.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ddee2150bdcb6622dcc6b5c93d0d1515b31137f32322196bf279647d670ac007
+size 2685894
diff --git a/S2OJ/1800/data/operator7.ans b/S2OJ/1800/data/operator7.ans
new file mode 100644
index 00000000..964d3b94
--- /dev/null
+++ b/S2OJ/1800/data/operator7.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:59f5c31ef0b7709d2af3d648c8eeacadce6d656dcd0b972f30a8ae9f90c5aa71
+size 953696
diff --git a/S2OJ/1800/data/operator7.in b/S2OJ/1800/data/operator7.in
new file mode 100644
index 00000000..1724c684
--- /dev/null
+++ b/S2OJ/1800/data/operator7.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:3ecc548b0e04fce71fb5ae27373b47b2f9682768cc4040d8362cac581f7d7fc2
+size 4280296
diff --git a/S2OJ/1800/data/operator8.ans b/S2OJ/1800/data/operator8.ans
new file mode 100644
index 00000000..29abd592
--- /dev/null
+++ b/S2OJ/1800/data/operator8.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:690e6ba3d2a5d88906889c7597561cbbfe40626078fb85c8c29530cfe4bfe9ce
+size 953245
diff --git a/S2OJ/1800/data/operator8.in b/S2OJ/1800/data/operator8.in
new file mode 100644
index 00000000..c7c18d16
--- /dev/null
+++ b/S2OJ/1800/data/operator8.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9906765430b322d8fa0f1fb25927cd54f8ea85a4205a734768547db26f0fb298
+size 4278831
diff --git a/S2OJ/1800/data/operator9.ans b/S2OJ/1800/data/operator9.ans
new file mode 100644
index 00000000..a423d38e
--- /dev/null
+++ b/S2OJ/1800/data/operator9.ans
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:858ba37496f9198e5fe01d907a94d46506f9b55f08fde074a309c48ccc89c139
+size 1889065
diff --git a/S2OJ/1800/data/operator9.in b/S2OJ/1800/data/operator9.in
new file mode 100644
index 00000000..65797d75
--- /dev/null
+++ b/S2OJ/1800/data/operator9.in
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:99007d8a4f16b06eee069778b9607906c3027525533534b1f1310aee02f23560
+size 7800336
diff --git a/S2OJ/1800/data/problem.conf b/S2OJ/1800/data/problem.conf
new file mode 100644
index 00000000..4e43762d
--- /dev/null
+++ b/S2OJ/1800/data/problem.conf
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:dcf908054c9da65549ec78e124325b36965e16b170b74eea5bafde282d233a88
+size 187