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

public class Solution {
static long sumOfGroup(int k) {
   int i,j;
   long t= ( (k-1)*(long)(k))/2;
   long at= 1+ (t-1)*2;
   long sum=((long)(k)*(long)(2* (at+2)+(k-1)*2))/2;
   return sum;
   }
   public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
       int k = in.nextInt();
       long answer = sumOfGroup(k);
       System.out.println(answer);
       in.close();
   }
}