def f(n)
  n /= 2 while n % 2 == 0
  n /= 5 while n % 5 == 0
  n == 1
end

def g(a, b)
  b *= 10 while a % b == 0
  a *= 10 while a % b != 0
  a / b % 10
end

N = gets.to_i
M = gets.to_i

denominator = M / N.gcd(M)
p f(denominator) ? g(N, M) : -1