L = int(input())
R = int(input())

prime = [ True ] * (R + 1)
prime[0], prime[1] = False, False
for i in range(2, R + 1):
	if prime[i]:
		for j in range(i * 2, R + 1, i):
			prime[j] = False

maxlen = 0
answer = -1
plist = list(filter(lambda x: prime[x], range(L, R + 1)))
for i in range(len(plist)):
	bit = 0
	pos = i
	while pos < len(plist):
		if ((bit >> (plist[pos] % 9)) & 1) == 1:
			break
		bit |= 1 << (plist[pos] % 9)
		pos += 1
	if maxlen <= pos - i:
		maxlen = pos - i
		answer = plist[i]

print(answer)