#include <iostream>

using namespace std;

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

    int st = 1;
    int dr = n;

    int sol = -1;

    while (st <= dr)
    {
        int mij = (st + dr) / 2;

        cout << "?" << ' ' << mij;
        cout.flush();

        int raspuns;
        cin >> raspuns;
        cout.flush();

        if (raspuns == 0)
        {
            st = mij + 1;
        }
        else if (raspuns == 1)
        {
            dr = mij - 1;
            sol = mij;
        }
    }

    cout << "!" << ' ' << sol << '\n';

    cout.flush();

    return 0;
}