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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 Star {
        Scanner in =new Scanner(System.in);
        public static void main(String args[]){
            new Star().go();
        }
        public void go(){
            int count=1;
            int prev=0;
                int a=in.nextInt();
                for(int i=1;i<= a-1;i++){
                    //int t=count;
                    count+=12*i;
                    //prev=t;
                    
                }
                System.out.println(count);
        }

}
