from fractions import gcd


def solve():
    N = int(input())
    M = int(input())

    g = gcd(N, M)
    n = N // g
    m = M // g

    o = m

    c2 = c5 = 0

    while o % 5 == 0:
        o //= 5
        c5 += 1

    while o % 2 == 0:
        o //= 2
        c2 += 1

    if o != 1:
        print(-1)
        return

    if c2 == c5:
        d = 1
    elif c2 > c5:
        d = 5
    else:
        c5 -= c2
        d = 2 ** c5 % 10

    n *= d
    while n % 10 == 0:
        n //= 10
    print(n % 10)


if __name__ == '__main__':
    solve()