#include<bits/stdc++.h>
using namespace std;
int main(){
	int ci=1,i=1,h=0,ch=1,n;
	cin>>n; 
	while(i<=n){
		while(ci<=i){
			ch=ch*ci;
			ci++;
		}
		h+=ch;
		i++;
	}
	cout<<h;
	return 0;
}

/**************************************************************
	Problem: 1019
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/