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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 Test {

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