#include <stdio.h>
int ans (int Z)
{
	int i,aux,p;
	int cont=0;
	for (i=1 ; cont<Z ; ++i)
	{
		p=i;
		while ((p/5 != 0)&&(p%5 == 0))
		{
			p/=5;
			++cont;
			aux=cont;
		}
	}
	p=cont-Z;
	if (p != 0)
		return -1;
	else
		return i-1;
}
int main ()
{
	int P;
	freopen ("fact.in","r",stdin);
	freopen ("fact.out","w",stdout);
	scanf ("%d",&P);
	printf ("%d\n", ans(P));
	return 0;
}