#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long n,p,i;
int main()
{
   f>>p;
   n=p*5;
   for (i=2;i<=n;i++)
   {
       if (n/(pow(5,i))>=1)
       n=n-pow(5,i)/5;
       else
       break;
   }
   if (n>=0)
   g<<n;
   else
   g<<-1;
   f.close();
   g.close();
    return 0;
}