#include <iostream>
using namespace std;

int main() {
    int req[2] = {500000000, 0}, res, next, obs = req[0]>>1, ans;
    while(1) {
        cout << "? " << req[0] << endl;
        cin >> res;
        next = req[0] + (res?obs:-obs);
        if(next==req[1]) {
            ans = req[0]>req[1]?req[1]:req[0];
            break;
        }
        obs = obs>1?obs>>=1:1;
        req[1] = req[0];
        req[0] = next;
    }
    cout << "! " << ans << endl;
}