#include <bits/stdc++.h>   using namespace std;   long long a, b, c, e[200000], mix, l, r, o, d[200000];   vector<long long> v[100000], v1;   set<long long> st;   map<long long, long long> mp, mp1;   string s;   pair<int, int> p[100000], p1[100000];   char ch[10];   deque<char> dq;   int main() {     cin >> a;     for (int i = 0; i < a / 4; i++)       if ((a - 2 * (i + 1)) % 2 == 0) c++;     if (a % 4 == 0) {       cout << c - 1;     } else       cout << c;   }   