def smallest_prime_factors(n):
    spf = [0]*(n+1)
    for i in range(n+1):
        spf[i] = i
    for i in range(2,n+1):
        if i*i>n:
            break
        if spf[i] == i:
            for j in range(i*i, n+1, i):
                if spf[j] == j:
                    spf[j] = i
    return spf

K = int(input())
N = int(input())
spf = smallest_prime_factors(N)

hash = []
prime = []
for i in range(K,N+1):
    if spf[i]==i and i!=1:
        num = i
        prime.append(num)
        while len(str(num))>1:
            num = sum([int(j) for j in str(num)])
        hash.append(num)
            
l,r = 0,0
res = 0
ans = 0
s = set()
while l<len(hash):
    while r<len(hash) and hash[r] not in s:
        s.add(hash[r])
        r += 1
    if r-l>=res:
        res = r-l
        ans = prime[l]
    s.remove(hash[l])
    l += 1
print(ans)