#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) {
    // Return the sum of the elements of the k'th group.
     long n=0;
    for (int i=0;i<=k;i++)
    {
     n=n+i;
    }
    long d=n*n;
    
    long n1=n-k;
    long d1=n1*n1;
    long ans=d-d1;
    return ans;
}

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