#include<bits/stdc++.h>
using namespace std;
int n,i=1,s,l=1,s1=1;
int main(){
	cin>>n;
	while(i<=n){
		l=1;
		s1=1; 
		while(l<=i){
			s1=s1*l;
			l++;
		}
		s=s+s1;
		i++;
	}
	cout<<s;
	return 0;
}
/**************************************************************
	Problem: 1019
	User: zhangziang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/