a = int(raw_input("factorial? "))
if a > 23:
	if a/25 == 0:
		c = int((a+1)%25)
	if a/25 != 0:
		c = int(a/25)
	b = (a/5)+c
	print b
else:
	if a == 0:
		print "1"
	else:
		print a/5