diff --git a/problem/P3865/P3865.cpp b/problem/P3865/P3865.cpp
new file mode 100644
index 00000000..ab074957
--- /dev/null
+++ b/problem/P3865/P3865.cpp
@@ -0,0 +1,24 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, m, l, r, k, t, f[100005][25];
+
+int main() {
+    scanf("%d%d", &n, &m);
+    for (int i = 1; i <= n; i++) {
+        scanf("%d", &f[i][0]);
+    }
+    t = log(n) / log(2) + 1;
+    for (int i = 1; i < t; i++) {
+        for (int j = 1; j <= n - (1 << i) + 1; j++) {
+            f[j][i] = max(f[j][i - 1], f[j + (1 << i - 1)][i - 1]);
+        }
+    }
+    for (int i = 1; i <= m; i++) {
+        scanf("%d%d", &l, &r);
+        k = log(r - l + 1) / log(2);
+        printf("%d\n", max(f[l][k], f[r - (1 << k) + 1][k]));
+    }
+    return 0;
+}