#include <fstream>
//LL 9223372036854775807 -9223372036854775808
using namespace std;

int main()
{
	long long n,k,p,s=0,m=0,i;
	ifstream f ("fact.in");
	ofstream g ("fact.out");
	f>>n;
	while (n)
	{
		k=1;
		p=0;
		i=0;
		while (p<=n)
		{
			s=p;
			i++;
			p=p+k;
			k=k*5;
		}
		if (p>=(n+i))
		{
			m=m+k/5;
			n=n-s;
		}
		else
		{
			n=0;
			m=-1;
		}
	}
	g<<m;
	
	f.close();
	g.close();
	return 0;
}