def is_prime(n):
    if n == 2:
        return True
    if n == 1 or n % 2 == 0:
        return False
    for i in range(3, int(n**0.5) + 1, 2):
        if n % i == 0:
            return False
    return True

a, b = map(int, input().split())

if a%2 == 0:
    for i in range(a+1, b + 1,2):
        if i%2 == 1 and is_prime(i):
            A = list(str(i))
            if A == A[::-1]:
                print(i)
else:
    for i in range(a, b + 1,2):
        if i%2 == 1 and is_prime(i):
            A = list(str(i))
            if A == A[::-1]:
                print(i)