#include <iostream>

using namespace std;

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

    int st = 1, dr = n;
    int mid, outcome;
    while (st <= dr) {
        mid = (st + dr) / 2;
        cout << "? " << mid << '\n';
        cout.flush();
        cin >> outcome;
        if (outcome == 0) {
            st = mid + 1;
        }
        else {
            dr = mid - 1;
        }
    }
    cout << "! " << st << '\n';
    cout.flush();
    return 0;
}