#include <fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long n,i,nr,y,p,p1;
int main ()
{
f>>p1;

n=5;
if (p1==0)
	 g<<"1\n";
	 else
	 {

do
{
nr=0;
p=5;
y=n;
while (y>=p)
			{
			nr=nr+y/p;
			p=p*5;
			}
if (nr<p1)
		n=n+5;
}
while (nr<p1);
if (nr==p1)
	 g<<n<<'\n';
	 else
	 g<<"-1\n";
   }
f.close ();
g.close ();
return 0;
}