#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) {
    long c,k0=k-1,sum=0,i;
    c=k0*(2+(k0-1))/2;
    for(i=0;i<k;i++)
    {
        sum=sum+(2*c+1);
        c++;
    }
    return sum;
    
    // Return the sum of the elements of the k'th group.
}

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