#include <iostream>

using namespace std;

int main()
{
    int n;
    cin >> n;
    int st = 0, dr = n, ok;

    while(st != dr)
    {
        int mid = (st + dr) / 2;
        cout << "? " << mid << endl;

        cin >> ok;

        if(ok == 0)
            st = mid + 1;
        else
            dr = mid;
    }
    cout << "! " << st << endl;
    return 0;
}