require 'prime'
a = gets.to_i
b = gets.to_i
g = a.gcd(b)
a/=g
b/=g
if(a%b==0)
  a /= b
  while (a%10==0) do
    a /= 10
  end
  puts a%10
  exit
end
_b = b
[2,5].each do |_p|
  while _b % _p==0 do
    _b /= _p
  end
end
if(_b==1)
  r = a.to_r / b
  while r % 1 > 0
    r %= 1
    r *= 10
  end
  puts (r % 10).to_i
else
  puts -1
end