max_n = 500000000
min_n = 0

fi = open('fact.in','r')
fo = open('fact.out','w')

p = int(fi.read())

def zer(n):
	cz = 0
	if n == 0:
		return 1
	while n != 0:
		cz = cz + (n//5)
		n = n//5
	return cz

if p == 0:
	mid_n = -1
else:
	while min_n < max_n:
		mid_n = (max_n + min_n) / 2
		tmp_res = zer(mid_n)
		if p < tmp_res:
			max_n = mid_n - 1
		elif p > tmp_res:
			min_n = mid_n + 1
		else:
			break
	else:
		mid_n = -1

#print(mid_n//5 * 5)
if mid_n == -1:
	fo.write(str(mid_n))
else:
	fo.write(str(mid_n//5 * 5))

fi.close()
fo.close()
	
	
#print(zer(a))