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 t_p_o_n=((k-1)*k)/2;
        //System.out.println(t_p_o_n);
        int s_p_o_n=t_p_o_n*t_p_o_n;
        //System.out.println(f_o_n);
        int s_t_o_n=(t_p_o_n+k)*(t_p_o_n+k);
        //System.out.println(l_o_n);
        int sum=s_t_o_n-s_p_o_n;
        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();
    }
}