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

object Problem253 {

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

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

  def waitBurnout(): Int = (1 to 50).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 = 50
    val max = Math.pow(10, 9).toInt
    searchR(min, max, 1)
  }

  def proc(): Int = {
    if (question(50) != -1) {
      // 二分探索
      search()
    } else {
      // 0以下の処理が面倒なので長さが50以下の場合は燃え尽きるまで待つ
      waitBurnout()
    }
  }

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