#include <bits/stdc++.h>
using namespace std;
bool trv[108][108];
int main() {
  int n;
  cin >> n;
  int res = 0;
  for (int l = 0; l < n; l++) {
    for (int r = l + 1; r <= n; r++) {
      if (trv[l][r]) continue;
      trv[l][r] = true;
      res++;
      for (int i = n; i > r; i--) {
        if (!trv[r][i]) {
          trv[r][i] = true;
          break;
        }
      }
    }
  }
  cout << res;
}
