#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
const int N = 1e6+10;
int t,n,m,k,l,r,op,x,y;
int f[N];
void solve(){
    while(cin>>n){
        if(n%2)cout<<0;
        else{
            n/=2;
            if((n+1)%2)n--;
            cout<<(n/2);
        }
        cout<<"\n";
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);  
    solve();
    return 0;
}