import sys
import math
import bisect
from heapq import heapify, heappop, heappush
from collections import deque, defaultdict, Counter
from functools import lru_cache
from itertools import accumulate, combinations, permutations, product

sys.setrecursionlimit(1000000)
MOD = 10 ** 9 + 7
MOD99 = 998244353

input = lambda: sys.stdin.readline().strip()
NI = lambda: int(input())
NMI = lambda: map(int, input().split())
NLI = lambda: list(NMI())
SI = lambda: input()
SMI = lambda: input().split()
SLI = lambda: list(SMI())
EI = lambda m: [NLI() for _ in range(m)]


# 高速エラストテネス　sieve[n]はnの最小の素因数
def make_prime_table(n):
    sieve = list(range(n + 1))
    sieve[0] = -1
    sieve[1] = -1
    for i in range(4, n + 1, 2):
        sieve[i] = 2
    for i in range(3, int(n ** 0.5) + 1, 2):
        if sieve[i] != i:
            continue
        for j in range(i * i, n + 1, i * 2):
            if sieve[j] == j:
                sieve[j] = i
    return sieve


# Nの素因数分解を辞書で返す(単体)
def prime_fact(n):
    root = int(n**0.5) + 1
    prime_dict = {}
    for i in range(2, root):
        cnt = 0
        while n % i == 0:
            cnt += 1
            n = n // i
        if cnt:
            prime_dict[i] = cnt
    if n != 1:
        prime_dict[n] = 1
    return prime_dict

# 約数列挙（単体）
def divisors(x):
    res = set()
    for i in range(1, int(x**0.5) + 2):
        if x % i == 0:
            res.add(i)
            res.add(x//i)
    return res


def h(x):
    while x >= 10:
        x = sum(int(s) for s in str(x))
    return x


def main():
    K = NI()
    N = NI()
    prime_table = make_prime_table(N+1)
    primes = [p for i, p in enumerate(prime_table) if i == p and K <= p <= N]
    H = [h(p) for p in primes]
    ans = 0
    for g in range(9, 0, -1):
        ok = False
        for i in range(len(H)+1-g):
            S = set(H[i:i+g])
            if len(S) == g:
                ans = max(ans, primes[i])
                ok = True
        if ok:
            break
    print(ans)


if __name__ == "__main__":
    main()