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

public class Solution {
    
    static long totalSum(long n){
        return (long)n*(long)n;
    }
    
    static long numberOfElements(long k){
        long result = 0;
        for(int i = 1; i <= k; i ++){
            result += i;
        }
        return result;
    }

    static long sumOfGroup(int k) {
        return totalSum(numberOfElements((long)k)) - totalSum(numberOfElements((long)k) -(long)k);
    }

    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();
    }
}