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

int ask(int x)
{
	static int cnt = 0;
	static map<int, int> cac;
	if (cac.count(x - cnt)) return cac[x - cnt];
	
	int res;
	cout << "? " << x - cnt++ << endl;
	cin >> res;
	return res;
}

int solve()
{
	if (ask(100) == 0) return 100;
	int l, r;
	if (ask(100) < 0) l = 0, r = 100;
	else l = 100, r = 1e9 + 10;
	while (true){
		int m = (l + r) / 2;
		if (ask(m) == 0) return m;
		if (ask(m) == -1) r = m;
		else l = m;
	}
}

int main()
{
	cout << solve() << endl;
}