#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,b=1,a=1,d=1,e=0;
    cin>>n;
    for(b;b<=n;b++){
    	d=1;
    	a=1;
    	for(a;a<=b;a++){
    		d=d*a;
    		
    	}
    	e=e+d;
    }
cout<<e;
}
/**************************************************************
	Problem: 1019
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/