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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 Problem0171b {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(triangular(n-1)*4 + (n*2-1)*(n*2-1));
    }
    public static int triangular(int n) {
        if(n == -1) {
            return 0;
        }
        int sum = 0;
        for(int i = 1; i <= n; i++) {
            sum+=i;
        }
        return sum;
    }
}
