from math import gcd
import sys
input = sys.stdin.readline

N = int(input())
M = int(input())
g = gcd(N, M)
N //= g
M //= g
while M % 5 == 0:
    M //= 5
    N *= 2
while M % 2 == 0:
    M //= 2
    N *= 5
if M != 1:
    print(-1)
    exit()
while N % 10 == 0:
    N //= 10
print(N % 10)