#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int sum = 0;
    int last = 0;
    last = 2 + (n-1)*3;
    sum = (2 + last) * n / 2;
    cout << sum << endl;
}
// 64 位输出请用 printf("%lld")