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

/**************************************************************
	Problem: 1019
	User: fzy001
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/