#include <fstream>
using namespace std;
ifstream in("factorial.in");
ofstream out("factorial.out");
int main()
{
	long int p,cinci,aux,plus,putere;
	in>>p;
	cinci=5;
	while(putere<p)
	{
		aux=cinci;
		plus=0;
		while(cinci%5==0)
		{
			++plus;
			cinci=cinci/5;
		}
		putere+=plus;
		cinci+=5;
	}
	if(p=0) 
		out<<"1";
	else 
		out<<putere;
	return 0;
}