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