#include <iostream>
using namespace std;
#include <fstream>
using namespace std;

int main()
{	fstream f,g;
f.open("fact.in",fstream::in);
g.open("fact.out",fstream::out);
	long int p,a,r,ax={0};
	f>>p;
	a=p*5;
	r=5;
	ax=a;
	while (r*5<a){
		r*=5;
		if (r==ax){
			a=-1;
			break;
		}
		a-=5;
	}
	if (p==0) g<<1;
	else g<<a;
	g.close();
	return 0;
}