#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,i,s=0,t=1;
    cin>>n;
    for(i=1;i<=n;i++){
        t*=i;
        s+=t;
    }
    cout<<s;
    return 0;
}
/**************************************************************
	Problem: 1019
	User: chenmingyu
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/