#include <bits/stdc++.h>

using namespace std;

long get_ith_odd_int(long pos)
{
    long result = 2*pos + 1;
    
    return result;
}

long sumOfGroup(int k) {
    // Return the sum of the elements of the k'th group.
    long idx = 1;
    long result = 0;
    for (int i = 1; i < k; i++)
    {
        idx += i;
    }
    //cout << "index " << idx << endl;
    for (int j = 0; j < k; j++)
    {
        //cout << "ith odd " << get_ith_odd_int(j+idx-1) << endl;
        result += get_ith_odd_int(j+idx-1);
    }
    return result;
}

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