#include <bits/stdc++.h>
using namespace std;
bool cmp(pair<int, int> a, pair<int, int> b) {
  return a.first < b.first ||
         a.first == b.first && a.second - a.first < b.second - b.first;
}
int main() {
  srand(time(0));
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long n, mod = 1e9 + 7, ans = 0;
  cin >> n;
  vector<pair<int, int>> A;
  for (int i = 0; i <= n; i++) {
    for (int j = 1; j <= n - i; j++) {
      A.push_back({j, j + i});
    }
  }
  sort(A.begin(), A.end());
  vector<bool> used(A.size(), 0);
  for (int i = 0; i < A.size(); i++) {
    for (int j = A.size() - 1; j >= 0; j--) {
      if (!used[j] && !used[i]) {
        if (A[i].second == A[j].first && A[j].second == n && A[i].first == 1) {
          used[i] = 1;
          used[j] = 1;
          ans++;
          break;
        }
      }
    }
  }
  for (int i = 0; i < A.size(); i++) {
    for (int j = A.size() - 1; j >= 0; j--) {
      if (!used[i] && !used[j]) {
        if (A[i].second == A[j].first) {
          used[i] = 1;
          used[j] = 1;
          ans++;
        }
      }
    }
  }
  for (int i = 0; i < A.size(); i++) {
    if (!used[i]) {
      ans++;
    }
  }
  cout << ans;
}
