import math

def gcd(n, m):
    if m == 0:
        return n
    return gcd(m, n % m)

def primes(m):
    max = math.floor(math.sqrt(m))
    nums = []
    for i in range(2, max):
        while m % i == 0:
            nums.append(i)
            m = m / i
    return nums

def isTerminate(p):
    setted = list(set(p))
    if 2 in setted:
        setted.remove(2)
    if 5 in setted:
        setted.remove(5)

    if len(setted) > 0:
        return False
    else:
        return True

n = int(input())
m = int(input())

g = gcd(n, m)

n = n // g
m = m // g

p = primes(m)

a = isTerminate(p)
if a:
    ans = n / m
    s_ans = str(ans)
    for i in range(len(s_ans) - 1, -1, -1):
        if s_ans[i] != '0' and s_ans[i] != '.':
            print(s_ans[i])
            break
else:
    print(-1)