#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,i=1,c=0;
    int s=1;
    cin>>n;
        while(i<=n){
        s=s*i;
        i++;
        c=c+s;
        }
    cout<<c;
return 0;
 
/**************************************************************
	Problem: 1019
	User: hongguangxi
	Language: C++
	Result: Compile Error
****************************************************************/