#include<fstream>
using namespace std;
long long n,p,i,g,q,s;
int main ()
{
	ifstream f("fact.in");
	ofstream f2("fact.out");
	f>>p;
	n=1;
	s=2;
	while(n<2000000 && !g)
	{   
		for(i=3;i<=n;i++)
			s=s*i;
	    if(s%10==0)
			while(s%10==0)
			{
				if(s%10==0)
					q++;
				s=s/10;
			}
		if(p==q)
		g=1;
		n++;
		s=2;
		q=0;
	}
	if(g)
		f2<<n-1;
	else
		f2<<'-1';
	return 0;
	
}