#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
Int ask(Int k){
  cout<<"? "<<k<<endl;
  return cin>>k,k;
}
signed main(){
  Int l=0,r=1e9+1;
  while(l+1<r){
    Int m=(l+r)>>1;
    if(ask(m)) l=m;
    else r=m;
  }
  cout<<"! "<<l<<endl;
  return 0;
}