import scala.io.StdIn._

object Main extends App {

  val Array(a,b) = readLine().split(" ").map(_.toInt)


  def solve(): Int = {
    for(i <- 1 to 10000)
      if(f(i, 0.08) == a && f(i, 0.1) == b) return i
    -1
  }

  def f(money: Int, tax: Double): Int =
    (money * tax).floor.toInt

  println(solve())

}

