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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.Scanner;

public class B {
    public static void main(String[] args) {
        long[] nums = new long[18258];
        nums[1] = 1;
        for(int i = 2; i < nums.length; i++)
            nums[i] = 12 * (i - 1);
        
        for(int i = 2; i < nums.length; i++)
            nums[i] += nums[i-1];
            
        Scanner in = new Scanner(System.in);
        int a = in.nextInt();
        System.out.println(nums[a]);
        
    }
}
