#include <iostream>
#include <algorithm>
#include <string>
#include <set>
using namespace std;

int main(){
    int left = 0, right = 1e9;
    while(left < right){
        int middle = (left + right) / 2;
        cout << "? " << middle << endl;
        bool response;
        cin >> response;
        if(response){
            left = middle;
        }else{
            right = middle - 1;
        }
    }
    cout << "! " << left << endl;
}