#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, isum = 0;
  cin >> n;
  if (n % 2 == 0)
    cout << ((n + 1) * (n + 1) - 1) / 4;
  else
    cout << ((n + 1) * (n + 1)) / 4;
}
