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

public class Solution {

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