#include <bits/stdc++.h>
using namespace std;
int n,ans;
int dg(int y){
	int x=0;
	if(y==1) return 1;
	else x=dg(y-1)*y;
	return x;
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		ans+=dg(i);
	}
	cout<<ans;
	return 0;
}
/**************************************************************
	Problem: 1296
	User: hongjiaming
	Language: C++
	Result: Wrong Answer
****************************************************************/