#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,ans=0;
  cin >> n;

  for(int i=1; i<=n; i++){
	ans += n + i;
	if(i == n) break;
  }
  
  cout << ans << endl;
  //ans = 1 + i
  //ans = 2 + i+1
  //ans = 3 + i+3
 return 0;
}
