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

public class Solution {

    static long sumOfGroup(long k) {
       
        long p=k-1;
        long s=(p)*(p+1)/2;
        long sum=0;
   //      System.out.println(p+" "+s);
        long n=2*s+1;
        for(int i=0;i<k;i++)
        {
            
            sum=sum+n;
            n=n+2;
        }
        return sum;
       
        
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextLong();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}