diff --git a/problem/P4939/P4939.cpp b/problem/P4939/P4939.cpp
index 7f1e0578..b7c918c7 100644
--- a/problem/P4939/P4939.cpp
+++ b/problem/P4939/P4939.cpp
@@ -2,78 +2,37 @@
 
 using namespace std;
 
-struct node {
-    int l, r;
-    int s, d;
+int n, m, op, x, y, t[10000005];
 
-    node() {}
-    node(int _l, int _r) {
-        l = _l;
-        r = _r;
-        s = d = 0;
-    }
-} tr[10000005 << 2];
-int n, m, op, x, y, k;
-
-void pushup(int u) {
-    tr[u].s = tr[u << 1].s + tr[u << 1 | 1].s;
+int lowbit(int k) {
+    return k & -k;
 }
 
-void pushdown(int u) {
-    if (!tr[u].d) return;
-    tr[u << 1].d += tr[u].d;
-    tr[u << 1].s += (tr[u << 1].r - tr[u << 1].l + 1) * tr[u].d;
-    tr[u << 1 | 1].d += tr[u].d;
-    tr[u << 1 | 1].s += (tr[u << 1 | 1].r - tr[u << 1 | 1].l + 1) * tr[u].d;
-    tr[u].d = 0;
+void add(int x, int v) {
+    for (int i = x; i <= n + 1; i += lowbit(i)) {
+        t[i] += v;
+    }
 }
 
-void build(int u, int l, int r) {
-    tr[u] = node(l, r);
-    if (l == r) {
-        return;
+int sum(int x) {
+    int ans = 0;
+    for (int i = x; i > 0; i -= lowbit(i)) {
+        ans += t[i];
     }
-    int mid = l + r >> 1;
-    build(u << 1, l, mid);
-    build(u << 1 | 1, mid + 1, r);
-}
-
-void modify(int u, int l, int r, int d) {
-    if (tr[u].l >= l && tr[u].r <= r) {
-        tr[u].d += d;
-        tr[u].s += (tr[u].r - tr[u].l + 1) * d;
-        return;
-    }
-    int mid = tr[u].l + tr[u].r >> 1;
-    pushdown(u);
-    if (l <= mid) modify(u << 1, l, r, d);
-    if (r > mid) modify(u << 1 | 1, l, r, d);
-    pushup(u);
-}
-
-int query(int u, int l, int r) {
-    if (tr[u].l >= l && tr[u].r <= r) {
-        return tr[u].s;
-    }
-    int mid = tr[u].l + tr[u].r >> 1;
-    int s = 0;
-    pushdown(u);
-    if (l <= mid) s += query(u << 1, l, r);
-    if (r > mid) s += query(u << 1 | 1, l, r);
-    return s;
+    return ans;
 }
 
 int main() {
     cin >> n >> m;
-    build(1, 1, n);
     for (int i = 0; i < m; i++) {
         cin >> op >> x;
         if (op == 0) {
             cin >> y;
-            modify(1, x, y, 1);
+            add(x, 1);
+            add(y + 1, -1);
         }
         else if (op == 1) {
-            cout << query(1, x, x) << endl;
+            cout << sum(x) << endl;
         }
     }
     return 0;