diff --git a/LibreOJ/2551/2551.cpp b/LibreOJ/2551/2551.cpp
new file mode 100644
index 00000000..a27a7e25
--- /dev/null
+++ b/LibreOJ/2551/2551.cpp
@@ -0,0 +1,91 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5,
+          K = 1e6 + 5;
+
+int n, m, a[N], cnt, root[N];
+
+struct node {
+    int l, r, siz;
+    long long sum;
+} tr[N << 5];
+
+int build(int l, int r) {
+    int p = ++cnt;
+
+    if (l == r) return p;
+
+    int mid = l + r >> 1;
+
+    tr[p].l = build(l, mid);
+    tr[p].r = build(mid + 1, r);
+
+    return p;
+}
+
+int insert(int p, int l, int r, int x) {
+    int q = ++cnt;
+
+    tr[q] = tr[p];
+    tr[q].siz++;
+    tr[q].sum += x;
+
+    if (l == r) return q;
+
+    int mid = l + r >> 1;
+
+    if (x <= mid) {
+        tr[q].l = insert(tr[p].l, l, mid, x);
+    } else {
+        tr[q].r = insert(tr[p].r, mid + 1, r, x);
+    }
+
+    tr[q].siz = tr[tr[q].l].siz + tr[tr[q].r].siz;
+    tr[q].sum = tr[tr[q].l].sum + tr[tr[q].r].sum;
+
+    return q;
+}
+
+long long query(int p, int q, int l, int r, int f, int k) {
+    int siz = tr[p].siz - tr[q].siz;
+    long long sum = tr[p].sum - tr[q].sum;
+
+    if (!siz) return 0;
+    if (l >= k + f) return sum - static_cast<long long>(2 * k + 2 * f + siz - 1) * siz / 2;
+    if (r <= k + f + siz - 1) return static_cast<long long>(2 * k + 2 * f + siz - 1) * siz / 2 - sum;
+
+    int siz_l = tr[tr[p].l].siz - tr[tr[q].l].siz;
+    int mid = l + r >> 1;
+
+    return query(tr[p].l, tr[q].l, l, mid, f, k)
+         + query(tr[p].r, tr[q].r, mid + 1, r, f + siz_l, k);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    root[0] = build(1, 1000000);
+
+    for (int i = 1; i <= n; i++) {
+        root[i] = insert(root[i - 1], 1, 1000000, a[i]);
+    }
+
+    for (int i = 1, l, r, k; i <= m; i++) {
+        cin >> l >> r >> k;
+
+        cout << query(root[r], root[l - 1], 1, 1000000, 0, k) << endl;
+    }
+
+    return 0;
+}
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