#include <iostream>
using namespace std;

int ask(int Y){
  cout<<"? "<<Y<<endl;
  int res;
  cin>>res;
  return res;
}

int main(){
  int res=100; //initial, sample
  int max=1e9;
  int min=10;
  int Y=(max-min)/2;
  int i=100;
  res=ask(Y);
  i--;
  while(i>0){
    if(res==0){
      break;
    } else if(res==1){
      min=Y;
      Y=(Y+(max-Y)/2);
      res=ask(Y);
      i--;
    } else if(res==-1){
      max=Y;
      Y=(Y-(Y-min)/2);
      res=ask(Y);
      i--;
    }
  }
  cout<<"! "<<Y<<endl;
  return 0;
}