r,a,b,c,d=raw_input().split()
r=int(r);a=int(a);b=int(b);c=int(c);d=int(d)
dist=(((c-a)**2)**0.5+((d-b)**2)**0.5)
fact=dist/(2*r)
if fact==int(fact):
	print int(fact)
else:
	fact=int(fact)
	print fact+1