#include <iostream>

using namespace std;

int n, k, x, ans;

int main() {
    cin >> n;
    int st = 1, dr = n, mid;
    while (st < dr) {
        mid = (st + dr) / 2;
        cout << "? " << mid;
        cin >> k;
        if (k == 0)
            st = mid + 1;
        else if (k == -1)
            return 0;
        else {
            dr = mid;
            ans = mid;

        cout.flush();
    }
    cout << "! " << ans;
    cout.flush();
    return 0;
}