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 ar = k*(k-1)/2+1;
        long sum=0;
        ar = 2*ar-1;
        for(long i=1;i<=k;i++)
        {
            sum += ar;
            ar +=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();
    }
}