#include<bits/stdc++.h>
using namespace std;
int digui(int n);
int main(){
    int n=0,s=0;
    cin>>n;
    for(int i=1;i<=n;i++){
        s=s+digui(i);
    }
    cout<<s<<endl;
}
int digui(int n){
    if(n==1)
        return 1;
    else
        return n+digui(n-1);
}
/**************************************************************
	Problem: 1148
	User: wangyichen2
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/