#include <bits/stdc++.h>

using namespace std;

int verif(int x) {
	cout << "? " << x << endl; // vrem sa dea flush
	cout.flush();

	int raspuns; cin >> raspuns;

	// -1 -> query invalid
	// 0 -> k > x
	// 1 -> k <= x

	return raspuns; 
}

void afis(int x) {
	cout << "! " << x << endl;
	cout.flush();
}

int main() {
	int n; cin >> n;
	// noi cautam o valoare ascunsa k intre [1, n]

	int rasp = 0;
	for(int pas = (1 << 30); pas > 0; pas /= 2) {
		if(rasp + pas <= n && verif(rasp + pas) == false) rasp += pas;
	}

	afis(rasp + 1); // echivalent cu afis(l) fiindca l == r

	return 0;
}