#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x;
  cin >> n;
  if (n % 2 == 0) {
    x = n / 2;
    cout << x * (x + 1);
  } else {
    x = (n + 1) / 2;
    cout << (x - 1) * x + x;
  }
  return 0;
}
