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

public class Solution {

    static long sumOfGroup(int k) {
          long j=k-1;long i=0;
         j=j*(j+1)/2;
       i=(2*(j+1))-1;
       
    long sum=0;
    for(j=i;k>0;j=j+2)
    {
        sum=sum+j;
        k--;
    }
    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();
    }
}