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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 a {
  public static void main(String args[]){
    Scanner scan = new Scanner(System.in);
    int n;
    n=scan.nextInt();
    System.out.println(6*n*(n-1)+1);
  }
}
