#12618: C++AC解
st990185@gmail.com
(風神)
#include <iostream>
using namespace std;
int pt(short in0){
int out=1 ;
for (short i=1 ;i<=in0 ;i++ ){
out *=5 ;
}
return out ;
}
int main()
{
int in0 ;
while (cin >>in0 ){
long long int out =0 ;
for (long long int i=1 ;pt(i) <=in0 && i<=13 ;i++ ){
out +=in0/pt(i) ;
}
cout <<out <<endl ;
}
}