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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) {
    Scanner in = new Scanner(System.in); 
    int n = in.nextInt();
    in.close();
    System.out.println(6 * n * (n - 1) + 1);
  }
}