AC了好吧

#include <iostream>
using namespace std;
long long cous(long long N) {
    if (N < 3) return 0;
    long long total = N * (N - 1) * (N - 2) / 6;
    long long k = N / 2;
    long long semicircle = N * k * (k - 1) / 2;
    return total - semicircle;
}

int main() {
    int N;
    while (cin >> N) {
        cout << cous(N) << endl;
    }
    return 0;
}