#!/usr/bin/env python3
import sys
input = sys.stdin.readline
from fractions import gcd

n = int(input())
m = int(input())
g = gcd(n, m)
n = n // g
m = m // g
twos = 0; fives = 0
while m % 2 == 0:
    m //= 2
    twos += 1
while m % 5 == 0:
    m //= 5
    fives += 1

if m == 1:
    if twos > fives:
        n *= pow(5, twos - fives)
    else:
        n *= pow(2, fives - twos)
    while n % 10 == 0:
        n //= 10
    print(n % 10)
else:
    print(-1)