require 'prime'
a = gets.to_i
b = gets.to_i
g = a.gcd(b)
a/=g
b/=g
if(a%b==0)
  puts (a/b)%10
  exit
end
pd = Prime.prime_division(b).map(&:first)
pd -= [2,5]
if(pd.empty?)
  r = a.to_r / b
  while r % 1 > 0
    r *= 10
  end
  puts (r % 10).to_i
else
  puts -1
end