from collections import deque


def list_primes(limit):
    primes = []
    is_prime = [True] * (limit + 1)
    is_prime[0] = False
    is_prime[1] = False

    for p in range(0, limit + 1):
        if not is_prime[p]:
            continue
        primes.append(p)
        for i in range(p * p, limit + 1, p):
            is_prime[i] = False

    return primes


def digits_sum(num):
    res = str(num)
    while len(res) != 1:
        res = sum(int(x) for x in res)
        res = str(res)
    return res


K = int(input())
N = int(input())
mx = 0
used = deque()
ans = 2
for p in list_primes(N)[::-1]:
    if p < K:
        break
    x = digits_sum(p)
    if x in used:
        while x != used.popleft():
            pass
    used.append(x)
    if len(used) > mx:
        mx = len(used)
        ans = p

print(ans)