import math
n = int(input())
m = int(input())

k = math.gcd(n, m)
n = n // k
m = m // k

x = m
t = 0
f = 0

while x % 2 == 0:
    x = x // 2
    t = t + 1

while x % 5 == 0:
    x = x // 5
    f = f + 1
    
while t < f:
    n *= 2
    m *= 2
    t += 1

while t > f:
    n *= 5
    m *= 5
    f += 1

while n % 10 == 0:
    n = n // 10
    
print(n % 10 if x == 1 else -1)