def main(n_):
    n = n_
    s = 2
    f = 0
    while s * s * s * s <= n:
        if not n % s:
            if s == 2:
                return 0
            n = n // s
            if n % s:
                return 0
            n = n // s
            if not n % s:
                return 0
            f = 1
            break
        s += 1
    if not f:
        return 0
    f = 0
    while s * s <= n:
        if not n % s:
            n = n // s
            if not n % s:
                return 0
            f = 1
            break
        s += 1
    if not f:
        return 0
    while s * s <= n:
        if not n % s:
            return 0
        s += 1
    return 1

l, r = list(map(int, input().split()))
if r - l >= 3000:
    m = 45
    l0 = (l + 44) // 45
    r0 = r // 45
    for t in range(l0, r0+1):
        s = 2
        f = 1
        while s * s <= t:
            if not t % s:
                f = 0
                break
            s += 1
        if f:
            print(45*t)
            break
else:
    for t in range(l, r+1):
        if main(t):
            print(t)
            break
    else:
        print(-1)