import sys
#sys.setrecursionlimit(n)
import heapq
import re
import bisect
import random
import math
import itertools
from collections import defaultdict, deque
from fractions import Fraction
from copy import deepcopy

a = int(input())
b = int(input())

c = Fraction(a, b)
aa = c.numerator
bb = c.denominator
d = bb
p2 = 0
p5 = 0
while(d % 2 == 0):
  d //= 2
  p2 += 1
while(d % 5 == 0):
  d //= 5
  p5 += 1
if d == 1:
  while(aa % 10 == 0):
    aa //= 10
  aa %= 10
  while(p2 > p5):
    aa = (aa * 5) % 10
    p5 += 1
  while(p5 > p2):
    aa = (aa * 2) % 10
    p2 += 1
  print(aa)
else:
  print(-1)