from sys import exit
from math import gcd

N = int(input())
M = int(input())
g = gcd(N, M)
N //= g
M //= g

while not N % 10:
    N //= 10

m = M
ct = {2: 0, 5: 0}
for x in (2, 5):
    while not m % x:
        m //= x
        ct[x] += 1

if m != 1:
    print(-1)
    exit()

if ct[2] <= ct[5]:
    for i in range(ct[5] - ct[2]):
        N *= 2
        if not N % 10:
            N //= 10
else:
    for i in range(ct[2] - ct[5]):
        N *= 5
        if not N % 10:
            N //= 10
print(N % 10)