#include <iostream>

using namespace std;

int main()
{
    long long int n, st, dr, m, r;

    cin >> n;
    cout.flush();
    st = 1; dr = n;
    while (st <= dr)
    {
        m = (st + dr) / 2;
        cout << "? " << m;
        cout.flush();
        cin >> r;
        if (r == 1)
            dr = m - 1;
        else
            if (r == 0)
                st = m + 1;
    }
    cout << "! " << st;
    return 0;
}