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

void pri(int x) {
	cout << "? " << x << endl;
}

void pri_(int x) {
	cout << "! " << x << endl;
}

void solve() {

	int n;
	cin >> n;

	pri(1);
	int x;
	cin >> x;
	int pre = x;

	if (x == 0) {
		pri_(1);
	} else {
		int le = 2, ri = n;
		while (le <= ri) {
			int mid = (le + ri) >> 1;
			pri(mid);
			cin >> x;
			if (x > pre) {
				le = mid + 1;
			} else if (x < pre) {
				ri = mid - 1;
			} else {
				pri_(mid);
				return;
			}
			pre = x;
		}
	}

}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int T = 1;
	while (T--) {
		solve();
	}

	return 0;
}