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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.*;

public class b {
  public static void main(String[] args) throws Throwable {
    int n = Integer.parseInt(
        new BufferedReader(new InputStreamReader(System.in)).readLine());
    System.out.println(6 * n * (n - 1) + 1);
  }
}
