#include <bits/stdc++.h>

using namespace std;

int st = 1, dr;

int main()
{
	cin >> dr;

	while (true)
	{
		if (st == dr)
		{
			cout << "! " << st << '\n';
			cout.flush();
			break;
		}

		int m = (dr + st) / 2;
		cout << "? " << m << '\n';
		cout.flush();

		int rasp;
		cin >> rasp;
		
		if (rasp == 1)
			dr = m;
		else if (rasp == 0)
			st = m + 1;
		else
			break;
	}

	return 0;
}