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) {
        int i,j,sum,p;
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] A = new int[n];
        int[] pro=new int[n];
        for(i=0;i<n;i++){
            for(j=0;j<n;j++){
                if(A[i]!=A[j]){
                    pro[i]=A[i]*A[j];
                }
            }
       
        }
        sum=0;
        for(i=0;i<n;i++){
            sum=sum+pro[i];
        }
        System.out.print(sum);
        in.close();
    }
}