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

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

def prime(n, m):
    if n < m:
        n, m = m, n
    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)):
        if N >= 10:
            N %= 10
        if tmp[2] > tmp[5]:
            for i in range(tmp[2] - tmp[5]):
                N *= 5
        elif tmp[2] < tmp[5]:
            for i in range(tmp[5] - tmp[2]):
                N *= 2
        ans = N % 10
    else:
        ans = -1
print(ans)