#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) {
    long long lastn=(long long)(k+1)*k-1;
    long long firstn=(long long)k*(k-1)+1;
    long long cnt=(long long)(lastn-firstn)/2+1;
    long long sum=(long long)cnt*(firstn+lastn)/2;
    return sum;
}

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