#include <bits/stdc++.h>
using namespace std;
void solve() {
  int a, ans = 1;
  cin >> a;
  for (int i = 1; i <= a; ++i) ans += (i - 1) * 12;
  cout << ans << "\n";
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) solve();
  return 0;
}
