#include <bits/stdc++.h>
using namespace std;
bool is_disjoint(pair<int, int> s1, pair<int, int> s2) {
  return s1.second == s2.first || s1.first == s2.second;
}
int main() {
  int n;
  scanf("%d", &n);
  vector<pair<int, pair<int, int> > > segments;
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j <= n; j++) {
      segments.push_back({j - i, {i, j}});
    }
  }
  sort(segments.begin(), segments.end());
  int layers = 1;
  vector<bool> vis(segments.size(), false);
  for (int i = (int)segments.size() - 2; i >= 0; i--) {
    if (vis[i]) {
      continue;
    }
    int chose = i;
    int max_len = 0;
    for (int j = i - 1; j >= 0; j--) {
      if (vis[j]) {
        continue;
      }
      if (is_disjoint(segments[i].second, segments[j].second)) {
        if (segments[i].first + segments[j].first >= max_len) {
          max_len = segments[i].first + segments[j].first;
          chose = j;
        }
      }
    }
    vis[chose] = true;
    layers++;
  }
  printf("%d\n", layers);
  return 0;
}
