/* [A][M][C][B][N] / [K][R][I][P][6][8] */
#include <bits/stdc++.h>
#pragma warning(disable : 4996)
using namespace std;
// Global variables
const char sp = ' ', nl = '\n';
const int MOD = 9001; // 666013 998244353 1000000007

bool query(int n) {
	cout << "? " << n << nl;
	bool ans; cin >> ans;
	cout.flush();
	return ans;
}

int main() {
	int n;
	cin >> n;
	int st(1), dr(n), mid, p(n + 1);
	while (st <= dr) {
		mid = (st + dr) / 2;
		if (query(mid)) p = mid, dr = mid - 1;
		else st = mid + 1;
	}
	cout << "! " << p << nl;
	cout.flush();
}