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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 cfBStar {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long ret = 1;
        for (int k = 1; k < n; k++) {
            ret += (2*k) * 6;
        }
        System.out.println(ret);
    }
}
