#include<iostream>
#include<fstream>
using namespace std;
long t,s,i;
int main ()
{
ifstream f("fact.in");
ofstream g("fact.out");
f>>t;
f.close();
if(t>1)
s=5*t;
for(i=25;i<=t;i=i+25)
	s=s+t/i;
if(!t) s=1;
g<<s;
g.close();
cout<<s;

}