diff --git a/problem/P7157/P7157.cpp b/problem/P7157/P7157.cpp
new file mode 100644
index 00000000..0d1b2bbf
--- /dev/null
+++ b/problem/P7157/P7157.cpp
@@ -0,0 +1,10 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int main() {
+    long long n, k;
+    cin >> n >> k;
+    cout << n * (n - 1) / 2 - k << endl;
+    return 0;
+}