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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.*;
public class P171B {
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        
        int A = in.nextInt();
        
        int ans = 1;
        for (int i = 1; i < A; ++i)
            ans += 12*i;
        
        System.out.println(ans);
    }
}
