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

object Problem253 {

  val threshold: Int = 50

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

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

  def waitBurnout(): Int = (1 to threshold + 1).find(x => question(0) == 0).get

  def search(): Int = {
    @tailrec
    def searchR(min: Int, max: Int, burned: Int): Int = {
      val mid = (min + max) / 2

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

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

  def proc(): Int = {
    question(threshold) match {
      case 1 => search() // 二分探索
      case 0 => threshold // 一回で当たった
      case -1 => waitBurnout() // 0以下の処理が面倒なので長さが閾値以下の場合は燃え尽きるまで待つ
    }
  }

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