import math

a = int(input())
b = int(input())
c = math.gcd(a, b)

a //= c
b //= c

b2 = b
five = 0
two = 0
while b2 % 5 == 0:
    five += 1
    b2 //= 5
while b2 % 2 == 0:
    two += 1
    b2 //= 2


if b2 != 1:
    print(-1)
    exit(0)

a *= 2**five
a *= 5**two

while True:
    if a % 10 != 0:
        print(a % 10)
        break
    a //= 10