/递推

#include<bits/stdc++.h>
using namespace std;
int dp[3005];
int main(){
    int n; cin >> n;
    dp[1] = 3;
    for(int i = 2;i <= n;i++) dp[i] = dp[i - 1] + 2 * (2 * i - 1);
    cout << dp[n];
    return 0;
}