#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(long long int k) {
    // Return the sum of the elements of the k'th group.
    long long int n=(k*(k+1))/2;
    long long int sn=n*n;
    long long int m=n-k;
    long long int sm=m*m;
    
    return sn-sm;
}

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