#include <bits/stdc++.h>

#define REP(i, n) for(int i = 0; i < (int)(n); ++i)
#define FOR(i, m, n) for(int i = (m); i < (int)(n); ++i)
#define INF 2000000000

#ifdef LOCAL
  #define eprintf(...) fprintf(stdout, __VA_ARGS__)
#else
  #define eprintf(...) 0
#endif

using namespace std;

typedef long long LL;
typedef unsigned long long ULL;
typedef unsigned int uint;

int ctoi(char c) {
  return c - '0';
}

template <class C>
void printContainer(C &container, const char *delim=",") {
  for(const auto &e : container) {
    std::cout << e << delim;
  }
  std::cout << "\n";
}

int main() {
  int n;
  cin >> n;
  //int ans = (n) * (n/2+1) + ((n%2) ? 0 : (n/2));
  int ans = (n+1) * n / 2;
  cout << ans << endl;
}