#include <bits/stdc++.h>
using namespace std;
int main() {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> v;
  v.push_back(1);
  v.push_back(2);
  if (n <= 2)
    cout << n << endl;
  else {
    for (int i = 3; i <= n; i++) {
      v.push_back(i + v[i - 2 - 1]);
    }
    cout << v.back() << endl;
  }
  return 0;
}
