#include <bits/stdc++.h>
using namespace std;
int num(int n){
    int r,i=1,cnt=0;
    if(n==1){
        r=1;
    }
    else{
        r=num(n-1)+n;
        n--;
    }
    return r;
}
int main(){
    int v,cnt=0;
    cin>>v;
    for(int i=1;i<=v;i++){
        cnt+=num(i);
    }
    cout<<cnt;
    return 0;
}
/**************************************************************
	Problem: 1148
	User: luyanchen
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/