#include <bits/stdc++.h>
using namespace std;
int main()
{
int n,ans;
while(cin>>n)
{
ans=0;
while(n)
{
n/=5;
ans+=n;
}
cout<<ans<<endl;
}
}
#include <bits/stdc++.h>
using namespace std;
int main()
{
int n,ans;
while(cin>>n)
{
ans=0;
while(n)
{
n/=5;
ans+=n;
}
cout<<ans<<endl;
}
}