#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n % 2 == 0) {
    if (n >= 8 && n % 4 == 0)
      cout << ((n / 4) - 1) << endl;
    else if (n > 4 && n < 8)
      cout << "1" << endl;
    else if (n <= 4)
      cout << "0" << endl;
    else
      cout << (n / 4) << endl;
  } else {
    cout << "0" << endl;
  }
  return 0;
}
