#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define lowbit(i) (i&-i)
#define rand() (myrand())
using namespace std;
mt19937 myrand(time(0));
int n, x;
void ask(int k) {
	cout << "? " << k << endl;
	cin >> x;
}
void solve() {
	cin >> n;
	ask(1);
	if (!x) {
		cout << "! 1" << endl;
		return;
	}
	int l = 2, r = n, last = x;
	while(l < r) {
		int mid = (l + r)>>1;
		ask(mid);
		if (last == x) {
			cout << "! " << mid << endl;
			return;
		}
		if (last) {
			if (x > last) l = mid + 1;
			else r = mid;
		} 
		else {
			last = x;
			ask(l);
			l++;
			if (last == x) {
				cout << "! " << mid << endl;
				return;
			}
			if (x < last) r = mid;
			else l = mid + 1;
		}
		last = x;
	}
	cout << "! " << l << endl;
}
signed main(void) {
	ios::sync_with_stdio(false);
	cin.tie(0);
	solve();
	return 0;
}