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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 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        
        int sum = 0;
        for(int i = 1; i <= n; i++) {
            if(i == 1) {
                sum += 1;
            }
            
            sum += 6 * 2 * (i-1);
        }
        
        System.out.println(sum);
    }

}
