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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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class B_171_Star {
	public static void main(String[] args) throws IOException {
		BufferedReader buf = new BufferedReader(
				new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(buf.readLine());
		int a = Integer.parseInt(st.nextToken());
		System.out.println(6 * a * (a - 1) + 1);
	}
}
