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

int main() {
	int left = 1;
	int right = 1e9+1;
	int limit = 100;
	while (limit-- && right-left!=1) {
		int mid = (left+right)/2;
		cout << "? " << mid << endl;
		int y;
		cin >> y;
		if (y) left = mid;
		else right = mid;
	}
	cout << left << endl;
}