N, M = int(input()), int(input())

def to_and_five(num, lists=[]):
    if num == 1:
        return lists
    if num % 2 == 0:
        return to_and_five(num // 2, lists + [2])
    if num % 5 == 0:
        return to_and_five(num // 5, lists + [5])
    return False

def prime(n, m):
    if not (tmp := n % m):
        return m
    else:
        return prime(m, tmp)
    
if N % M == 0:
    ans = N // M
    while not ans % 10:
        ans //= 10
    ans %= 10
else:
    N, M = N // (tmp := prime(N, M)), M // tmp
    if (tmp := to_and_five(M)):
        N %= 10
        for i in tmp:
            if i == 5:
                N *= 2
            else:
                N *= 5
            N %= 10
        ans = N
    else:
        ans = -1
print(ans)