#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <cstdio>
#include <set>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
const int INF = 1e9;


int ask(int Y){
	cout << "? " << Y << endl;
	int res;
	cin >> res;
	return res;
}

int main(){

	int l = 0; int r = INF + 1;
	rep(i, 50){
		int mid = (l + r) / 2;
		if(ask(mid) == -1){//短い
			r = mid;
		}else if(ask(mid) == 1){//長い
			l = mid - 1;
		}else if(ask(mid) == 0){
			printf("! %d\n", max(0, mid - 1));
			return 0;
		}
	}
	for (int i = l - 10; i <= r; ++i){
		if(ask(i) == 0){
			printf("! %d\n", max(0, i - 1));
			return 0;
		}
	}

	return 0;
}