#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int64_t k) {
    int64_t s = (k * (k - 1)) >> 1;
    int64_t s1 = s * s;
    int64_t s2 = (s + k) * (s + k);
    return s2 - s1;
}

int main() {
    int k;
    cin >> k;
    long answer = sumOfGroup(k);
    cout << answer << endl;
    return 0;
}