import math

num = int(input())
den = int(input())

g = math.gcd(num,den)

num //= g
den //= g

d = den + 0

while d % 5 == 0:
    d //= 5
while d % 2 == 0:
    d //= 2

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

while num % den != 0:
    num *= 10

res = num // den
while res % 10 == 0:
    res //= 10
print(res%10)