#include <bits/stdc++.h>
using namespace std;

using ll = long long;

#define all(a) a.begin(),a.end();
#define rev(a) a.end(),a.begin();


void solve(){


   int n;cin>>n; 
   cout<<((n+1)*(n+2)/2)<<"\n";

}



int main()
{
   
    int t=1; 
    while(t--){
         solve();
    }


    return 0;
    
}