CodeForces 610A Pasha and Stick

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

int n,ans;

int main()
{
    while(~scanf("%d",&n)){
        ans=0;
        if(n%2!=0)ans=0;
        else ans=(n/2-1)/2;
        printf("%d\n",ans);
    }
    return 0;
}