#include <bits/stdc++.h>
int main() {
  int n;
  std::cin >> n;
  int sum = 0;
  for (int i = 1; i <= n; ++i) {
    int min;
    if (i < n - i + 1)
      min = i;
    else
      min = n - i + 1;
    sum += min;
  }
  std::cout << sum << "\n";
}
