#include <iostream>

using namespace std;

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

    int st(1), dr(n), ans(-1);

    while (st <= dr)
    {
        int mid = (st + dr) >> 1;
        cout << "? " << mid << endl;
        int flag;
        cin >> flag;
        if (flag == 0)
        {
            ans = mid + 1;
            st = mid + 1;
        }
        else
        {
            dr = mid - 1;
        }
    }
    cout << "! " << ans << endl;
    return 0;
}