import scala.annotation.tailrec
import scala.io.StdIn

object Problem246 {

  def question(mid: Int): Int = {
    println("? " + mid)
    StdIn.readInt()
  }

  def answer(result: Int): Unit = {
    println("! " + result)
  }

  def proc(): Int = {
    @tailrec
    def q(min: Int, max: Int): Int = {
      val mid = Math.round((min + max) / 2.0).toInt

      if (min == max) {
        return mid
      }

      question(mid) match {
        case 1 => q(mid, max)
        case 0 => q(min, mid - 1)
      }
    }

    val min = 1
    val max = Math.pow(10, 9).toInt
    q(min, max)
  }

  def main(args: Array[String]) {
    val result = proc()
    answer(result)
  }
}