#include<bits/stdc++.h>
using namespace std;
int n,s=0;
int f(int x){
    if(x==1) return 1;
    else return f(x-1)+x;
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        s=s+f(i);
    }
    cout<<s; 
    return 0;
}
/**************************************************************
	Problem: 1148
	User: chenlingxuan
	Language: C++
	Result: Accepted
	Time:19 ms
	Memory:2072 kb
****************************************************************/