#include <iostream>
using namespace std;


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

    int left = 1, right = n;

    while (left != right) {
        int mid = (left + right) / 2;

        cout << "? " << mid << "\n";
        cout.flush();

        int resp;
        cin >> resp;

        if (resp == 0)
            left = mid + 1;
        else
            right = mid;
    }

    cout << "! " << left << "\n";
    cout.flush();

    return 0;
}