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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 Star{

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long ans = 1;
        long g = 0;
        for( int i = 2; i <= n; i++){
            g += 12;
            ans += g;      
        }
        System.out.println(ans);

    }
}