diff --git a/S2OJ/399/399.cpp b/S2OJ/399/399.cpp
new file mode 100644
index 00000000..11e63cb7
--- /dev/null
+++ b/S2OJ/399/399.cpp
@@ -0,0 +1,35 @@
+#include <algorithm>
+#include <iostream>
+#include <limits>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n;
+long long sum[N], ans = std::numeric_limits<int>::min();
+std::pair<int, int> a[N];
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i].first >> a[i].second;
+    }
+
+    std::sort(a + 1, a + 1 + n, [](std::pair<int, int> a, std::pair<int, int> b) -> bool {
+        return a.first + a.second < b.first + b.second;
+    });
+
+    for (int i = 1; i <= n; i++) {
+        sum[i] = sum[i - 1] + a[i].first;
+        ans = std::max(ans, sum[i - 1] - a[i].second);
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}