K,N = int(input()),int(input())
primes = []
for i in range(max(2,K),N + 1):
	j = 2
	flag = True
	while j * j <= i:
		if i % j == 0:
			flag = False
			break
		j+=1
	if flag:
		primes.append(i)
def hash(prime):
	while prime >= 10:
		tmp = prime
		digitSum = 0
		while tmp > 0:
			digitSum += tmp % 10
			tmp //= 10
		prime = digitSum
	return prime
hashes = [hash(p) for p in primes]
used = [0 for i in range(10)]
left,right = 0,0
L = len(hashes)
used[hashes[left]]+=1
maxLen = 0
ans = 0
while left < L:
	while right + 1< L and used[hashes[right + 1]] == 0:
		right+=1
		used[hashes[right]]+=1
		if maxLen <= right - left + 1:
			maxLen = right - left + 1
			ans = primes[left]
	used[hashes[left]]-=1
	left+=1
print(ans)