#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: huanglingkai
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/