#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(long k) {
         long  i;
    long long val,sum=0;
    val=(k-1)*k/2;
    for(i=0;i<k;i++)
    {
        sum=sum+2*val+1;
        val=val+1;
    }
    return sum;
    // Return the sum of the elements of the k'th group.
}

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