#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int ans = 0;
  if (n == 1) {
    cout << 1 << endl;
    return 0;
  }
  if (n == 2) {
    cout << 2 << endl;
    return 0;
  }
  for (int i = n; i > n / 2; i--) ans += n + 1 - i;
  for (int i = 1; i < n / 2 + 1; i++) ans += i;
  cout << ans << endl;
}
