/*
    Author: Maksym Strelbitskyi
    Vinnytsia - 2016
*/

#define _CRT_DISABLE_PERFCRIT_LOCKS
#define _CRT_SECURE_NO_WARNINGS
#pragma comment (linker, "/STACK:64000000")

#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

using namespace std;

#define forn(m,n)   for (int i=(m); i<(n); i++)
#define form(k,m)   for (int j=(k); j<(m); j++)
#define uint        unsigned int
#define int64       long long int
#define uint64      unsigned long long int
#define bool        unsigned char
#define vi          vector<int>
#define vi64        vector<long long int>
#define vb          vector<bool>
#define vs          vector<string>
#define si          set<int>
#define pi          pair<int,int>
#define mp          make_pair
#define EPS         0.0000001
#define MOD         1000000007
#define true        1
#define false       0

template <class T> T gcd(T a, T b) {
	while (b) { a %= b; swap(a, b); } return a;
}

void solve() {
	// solution
	int n;
	cin >> n;
	if (n % 2 || n < 6)
	{
		cout << 0;
		return;
	}
	n /= 2;
	if (n % 2 == 0) --n;
	cout << n / 2;
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
#ifdef MYDEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	unsigned int start = clock(), fin;
#endif
	solve();
#ifdef MYDEBUG
	fin = clock();
	cout << "\n\nTime: " << fin - start << " ms.";
#endif
	return 0;
}