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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.*;import java.util.*;public class j{public static void main(String a[])throws IOException{Scanner b=new Scanner(System.in);double m=b.nextDouble();System.out.print((long)(6*m*(m-1)+1));}}