#include<bits/stdc++.h>
using namespace std;
int f(int n){
	int r=0;
	if(n==1) r=1; 
	else{
		r=f(n-1)+n;
	}
	return r;
}
int main(){
	int n,s=0;
	cin>>n;
	for(int i=1;i<=n;i++){
		s=s+f(i);
	} 
	cout<<s;	

}

/**************************************************************
	Problem: 1148
	User: wuweimo
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/