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