#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using ld=long double;
using ull=unsigned long long;
using pii=pair<int,int>;
using pll=pair<ll,ll>;
using mint=modint998244353;
const ll INF=1ll<<60;
int main(){
  ull N; cin>>N;
  if(N%2==0)cout<<(N+1)*(N/2)<<endl;
  else cout<<N*((N+1)/2)<<endl;
}