import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    def hash(x):
        if x < 10: return x
        if x in memo: return memo[x]
        res = memo[x] = hash(sum(int(c) for c in str(x)))
        return res

    memo = {}

    k = II()
    n = II()
    prime = [0, 1] * 100005
    prime[1] = 0
    prime[2] = 1
    for x in range(3, 200005):
        if x ** 2 > 200005: break
        if prime[x]:
            for y in range(x ** 2, 200005, x):
                prime[y] = 0
    xx = []
    hh = []
    for x in range(k, n + 1):
        if prime[x]:
            h = hash(x)
            xx.append(x)
            hh.append(h)
    #print(xx)
    #print(hh)
    mx_len = 0
    ans_x = 0
    last_pos = [-1] * 10
    l = 0
    for r, h in enumerate(hh):
        if last_pos[h] >= l:
            length = r - last_pos[h]
            l = last_pos[h] + 1
        else:
            length = r - l + 1
        if length >= mx_len:
            mx_len = length
            ans_x = xx[r - length + 1]
        last_pos[h] = r
    #print(mx_len)
    print(ans_x)

main()