#include <fstream>
#include <iostream>
#include <math.h>

using namespace std;
int main()
{
    long p,n,putere,cinci;
    ifstream f("fact.in");
    f>>p;
    f.close();
    n=0;putere=1;
while(p>1)
{putere=1;
while (putere<p)
         putere=putere*5;
p=p-putere/5;
n=n+putere;}
          
            
       

ofstream g("fact.out");
g<<n;
g.close();
      return 0;
}