#include <bits/stdc++.h>
using namespace std;
const string QUERY_PREF = "? ";
const string ANS_PREF = "! ";

int main() {
    int n;
    cin >> n;

    int le = 1, ri = n, target = 1;
    while (le <= ri) {
        int mid = (le + ri) / 2;
        cout << QUERY_PREF << mid << endl;

        int ans;
        cin >> ans;
        assert(ans != -1);
        if (ans == 1) {
            ri = mid - 1;
            target = mid;
        } else {
            le = mid + 1;
        }
    }
    cout << ANS_PREF << target << endl;
    return 0;
}