#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: houshanglin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/