#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int arr[n + 1];
  memset(arr, 0, sizeof(arr));
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= n - i; j++) {
      for (int k = 0; k < i; k++) {
        arr[j + k]++;
      }
    }
  }
  int ans = 0;
  for (int i = n; i >= 0; i--) {
    ans = max(ans, arr[i]);
  }
  cout << ans << endl;
  return 0;
}
