#include <fstream.h>
int main (){
int n,p,cinci,n1;
fstream f1("fact.in",ios::in);
fstream f2("fact.out",ios::out);
f1>>p;
n=1;
cinci=0;
if (p>0) {
while (cinci<p)
   {
	if (cinci<p)
	n1=n;
	while (n1%5==0) {
	cinci++;
	n1=n1/5;
	}
   n++;
   }
n=n-1;
}
f2<<n;
return 0;
}