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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 B {
	public static void main(String[] args) {
		long r = 1;
		for (long n = new Scanner(System.in).nextLong(); n-- > 1;) {
			r += 12 * n;
		}
		System.out.println(r);
	}
}
