#include <bits/stdc++.h>
using namespace std;

int main(){
    int head_num = 100000000;
    int tail_num = 0;
    for(int i=0; i<100; i++){
        int num = (head_num + tail_num) / 2;
       cout << "? " << num << endl;
        int tmp;
        cin >> tmp;
        if(tmp == 1){
            if(tail_num == num){
                cout << num << endl;
                return 0;
            }
            tail_num = num;
        }else{
            if(head_num == num){
                cout << num << endl;
                return 0;
            }
            head_num = num;
        }
    }
    cout << head_num << endl;

    return 0;
}