#include <bits/stdc++.h>

#define ll long long


using namespace std;

const ll N = 1e6 + 10, MM = 1e9 + 7, MAX = 1e18;

int ask(int x) {
	cout << "? " << x << endl;
	int y; cin >> y;
	return y;
}

int solve() {
	int n; cin >> n;
	int l = 1, r = n;
	int res = 0;
	int cur = 0;
	while (l <= r) {
		int mid = l + r >> 1;
		int y = ask(l);
		if (y == cur) {
			res = l;
			break;
		}
		int y1 = ask(mid);
		if (y1 == y) {
			res = mid;
			break;
		}
		if (y1 == cur) {
			r = mid - 1;
			l++;
		}
		else {
			l = mid + 1;
		}
	}
	cout << "! " << res << endl;
	return 0;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int t = 1;
	//cin >> t;
	int i = 1;
	while (t--) {
		//cout << "case " << i << ": ";
		solve();
	}
	return 0;
}
/*

*/