#include <fstream>

using namespace std;

int main() {
	int p,n,c5,c2,m,k;
	
	ifstream f("fact.in");
	ofstream g("fact.out");
	
	f>>p;
	
	c2=0; c5=0; m=0;
	n=1;
	
	while (m<p)	{
		n++;
		k=n;
		while (k%2==0) {
			c2++;
			k=k/2;
		}
		while (k%5==0) {
			c5++;
			k=k/5;
		}
		if (c2>c5)
			m=c5;
		else
			m=c2;
	}
	
	if (m==p)
		g<<n;
	else
		g<<-1;
	
	g.close();
	
	return 0;
}