#include <iostream>

using namespace std;

int query(int x) {
	cout << "? " << x << '\n';
	cout.flush();
	cin >> x;
	return x;
}

int32_t main() {
	int n;
	cin >> n;

	int l = 1, r = n;

	while (l <= r) {
		int mid = (l + r) / 2;
		if (!query(mid))
			l = mid + 1;
		else
			r = mid - 1;
	}
	cout << "! " << l << '\n';
	cout.flush();

	return 0;
}