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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 Star {
	public static void main(String[] args){
		Scanner reader = new Scanner(System.in);
		int n = reader.nextInt();
		long[] memo = new long[n+1];
		memo[1] = 1;
		for(int i = 2; i <= n; i++)
			memo[i] = memo[i-1] + 12l*(i-1);
		System.out.println(memo[n]);
	}
}
