from fractions import gcd


def sieve(n):
    s = [True] * n
    for x in range(2, int(n ** 0.5) + 1):
        if s[x]:
            for i in range(x + x, n, x):
                s[i] = False
    return [i for i in range(n) if s[i] and i > 1]


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

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

    if m == 1:
        while n % 10 == 0:
            n //= 10
        print(n % 10)
        return

    o = m

    c2 = c5 = 0

    while True:
        p, y = divmod(o, 5)
        if y:
            break
        o = p
        c5 += 1

    while True:
        p, y = divmod(o, 2)
        if y:
            break
        o = p
        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()