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Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13

import java.util.Scanner;
public class main {

    public static void main(String[] args) {
      Scanner s = new Scanner (System.in);
int n= s.nextInt();int ans=0;
n --;
    for(int i=1; i<=n; i++)
        ans += (12 * i);
        System.out.println(ans+1);
    
    }
    
}
