#include <string>
#include <bitset>
#include <iostream>
#include <vector>
#include <set>
#include <algorithm>

using namespace std;

int main()
{
    long long n;
    cin>>n;
    n--;
    long long first = (n * (n + 1)) / 2;
    first = 2 * first + 1;
    unsigned long long sum = 0;
    for(int k = 0; k <= n; k++)
    {
        //cout<<first<<endl;
        sum += first;
        first += 2;
    }
    cout<<sum<<endl;
    return 0;
}