from collections import defaultdict
def SieveofEratosthenes(N):
    P = [0] * (N+1)
    P[0] = P[1] = -1
    for i in range(2,N+1):
        if P[i] == 0:
            k = i
            while k <= N:
                P[k] = i
                k += i
            P[i] = 0
    return P

def hash(N):
    if N in dic:
        return dic[N]
    x = N
    S = 0
    while x:
        S += x % 10
        x //= 10
    dic[N] = hash(S)
    return dic[N]

K = int(input())
N = int(input())
P = SieveofEratosthenes(N)
C = []
for i in range(K,N+1):
    if P[i] == 0:
        C.append(i)
dic = {}
for i in range(10):
    dic[i] = i
M = len(C)
F = []
for i in range(M):
    F.append(hash(C[i]))
dic = defaultdict(int)
Left = 0
Length = 0
ans = 0
for Right in range(M):
    dic[F[Right]] += 1
    while dic[F[Right]] >= 2:
        dic[F[Left]] -= 1
        Left += 1
    if Right - Left + 1 >= Length:
        Length = Right - Left + 1
        ans = C[Left]
print(ans)