//NOIP 1998普及组 T2
#include<bits/stdc++.h>
using namespace std;
using ll=long long;;
ll a[51],b[51],n;
signed main() {
    a[0]=1;
    for (int i=1;i<51;i++) {
        a[i]=a[i-1]*i;
        b[i]=b[i-1]+a[i];
    }
    cin>>n;
    cout<<b[n]<<endl;
}
//
// Created by Lenovo on 25-8-1.
//