#include<iostream>
#include<cstdio>
using namespace std;
 
int main(){
  int i,j,n,ans[100000],calc[100000];
 
  calc[0]=2;
  for(i=1;i<100000;i++)calc[i]=calc[i-1]+1;
  ans[1]=2;
  for(i=2;i<100000;i++)ans[i]=ans[i-1]+calc[i-2];
 
  while(cin >> n){
    cout << ans[n] << endl;
 
  }
 
}
