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

public class Calculator {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        int i=-1;int sum=0;
       for(int j=1;j<k;j++)
       {
           for(int l=1;l<=j;l++)
           {
               i=i+2;
           }
       }
        for(int j=0;j<k;j++)
        {
            i=i+2;
            sum=sum+i;
        }
        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();
    }
}