#include <iostream>

using namespace std;

int n;

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