#include<bits/stdc++.h>
using namespace std;
//5+55+555+5555+55555
int n,s,i;
int ss(int x){
	//如果为班长，返回x
	//否则返回下级+x 
	if(x==1) return 1; 
	else return ss(x-1)+x;
}
int main(){
	cin>>n;
	for(i=1;i<=n;i++){
		s+=ss(i);	
	}
	cout<<s;
return 0;}

/**************************************************************
	Problem: 1148
	User: fzy001
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/