#include <iostream>

using namespace std;

int n;

int main()
{
    cin >> n;

    int st = 1, dr = n, poz = -1;
    while(st <= dr)
    {
        int ans, mij = (st + dr) / 2;

        cout << "?" << mij << endl;
        cin >> ans;

        if(ans == 1)
        {
            dr = mij - 1;
            poz = mij;
        }

        else
            st = mij + 1;
    }

    cout << "!" << poz << endl;
    return 0;
}