import java.io.{BufferedReader, InputStreamReader}

import scala.annotation.tailrec

object Problem253 {

  val br = new BufferedReader(new InputStreamReader(System.in))

  def question(len: Int): Int = {
    println("? " + len)
    System.out.flush()
    br.readLine().toInt
  }

  def answer(len: Int): Unit = {
    println("! " + len)
    System.out.flush()
  }

  def waitBurnout() = while (question(0) != 0) {}

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

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

    val min = 100
    val max = Math.pow(10, 9).toInt
    searchR(min, max)
  }

  def main(args: Array[String]): Unit = {
    if (question(101) != -1) {
      val result = search()
      answer(result)
    } else {
      // 0以下の処理が面倒なので長さが100以下の場合は燃え尽きるまで待つ
      waitBurnout()
      answer(0)
    }
  }
}