import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextInt();
      long t= k*(k-1)+1;
     long z=t;
        long m=0;
        for(int i=1;i<k;i++){
          z=z+2;
            m=m+z;
            
        } 
        System.out.println(m+t);
    }
}