diff --git a/31xxx/31000.cpp b/31xxx/31000.cpp
new file mode 100644
index 00000000..b1c863f1
--- /dev/null
+++ b/31xxx/31000.cpp
@@ -0,0 +1,23 @@
+#include <iostream>
+using namespace std;
+
+void solve(void) {
+  int n; cin >> n;
+
+  int ans = (2*n+1)*(2*n+1);
+  for (int a=-n; a<=n; a++) {
+    if (a == 0) continue;
+    for (int b=-n; b<=n; b++) {
+      if (-n <= 1-a-b && 1-a-b <= n) ans++;
+    }
+  }
+  cout << ans;
+}
+
+int main(void) {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+
+  solve();
+  return 0;
+}
\ No newline at end of file