#include <iostream>

using namespace std;

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

    int from = 1, to = n;

    while(from < to)
    {
        int mid = (from + to) / 2;

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

        int answer;
        cin >> answer;

        if(answer == 1)
        {
            to = mid;
        }
        else
        {
            from = mid + 1;
        }
    }

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

    return 0;
}