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

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] m = new int[n];
        for(int m_i=0; m_i < n; m_i++){
            m[m_i] = in.nextInt();
        }
        long sum=0l;
        int x=1;
        while((n-x)>0)
            {
            sum+=(n-x)*(n-x-1);
            sum+=1;
            x++;
        }
        System.out.println(sum);
        // your code goes here
    }
}