import math
from collections import defaultdict as ddict
def sieve (n):
	check = [1]*(n+1)
	check[0] = check[1] = 0
	for d in xrange(2,int(math.sqrt(n))+1):
		if check[d] == 0: continue
		for comp in xrange(d*2,n+1,d):
			check[comp] = 0
	return check
def convert(n):
	while n > 9:
		tmp = 0
 		while n > 0:
 			tmp += n%10
 			n /= 10
 		n = tmp
 	return n
K = int(raw_input())
N = int(raw_input())
prime = sieve(N)
l = [i for i in xrange(K,N+1) if prime[i]]
ulhash = ddict(int)
ans = l[0]
maxlen = 1
ulhash[convert(l[0])] = lpos = 0
for rpos in xrange(1,len(l)):
	r = convert(l[rpos])
	if ulhash[r] >= lpos:
		lpos = ulhash[r] + 1
	ulhash[r] = rpos
	if maxlen <= rpos - lpos + 1:
		ans = l[lpos]
		maxlen = rpos - lpos + 1
print ans