diff --git a/S2OJ/400/400.cpp b/S2OJ/400/400.cpp
new file mode 100644
index 00000000..4e479464
--- /dev/null
+++ b/S2OJ/400/400.cpp
@@ -0,0 +1,56 @@
+#pragma GCC optimize("Ofast")
+
+#include <algorithm>
+#include <cstdio>
+#include <cstring>
+#include <vector>
+
+const int N = 1005;
+
+int n, m;
+long long g[N][N], l, r;
+bool vis[N][N];
+
+bool check(long long x) {
+    memset(vis, 0x00, sizeof(vis));
+
+    for (int i = 1; i <= n; i++) {
+        std::vector<long long> t;
+
+        for (int j = 1; j <= m; j++) {
+            if (g[i][j] >= x) t.push_back(j);
+        }
+
+        for (int j = 0; j < t.size(); j++) {
+            for (int k = j + 1; k < t.size(); k++) {
+                if (vis[t[j]][t[k]]) return true;
+                vis[t[j]][t[k]] = true;
+            }
+        }
+    }
+
+    return false;
+}
+
+int main() {
+    scanf("%d%d", &n, &m);
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= m; j++) {
+            scanf("%lld", &g[i][j]);
+            r = std::max(r, g[i][j]);
+        }
+    }
+
+    while (l <= r) {
+        long long mid = l + r >> 1;
+        if (check(mid)) {
+            l = mid + 1;
+        } else {
+            r = mid - 1;
+        }
+    }
+
+    printf("%lld\n", r);
+
+    return 0;
+}