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