#include<bits/stdc++.h>
using namespace std;
int n;
unsigned long long ans=0;
unsigned long long ans1=1;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		ans1=1;
		for(int j=1;j<=i;j++){
			ans1*=j;
			//cout<<"ans1:"<<ans1<<endl; 
		}
		ans+=ans1;
		//cout<<"ans:"<<ans<<endl;
	}
	cout<<ans<<endl;
	return 0;
}