#include <bits/stdc++.h>

using namespace std;

int N;

int query(int val)
{
    cout << '\n' << '?' << ' ' << val << '\n';
    int x;
    cin >> x;
    return x;
}

int main()
{
    cin >> N;
    int st = 1, dr = N;
    int retine = 0;
    while(st <= dr)
    {
        int mid = (st + dr) >> 1;
        int v = query(mid);
        if(v == 0)
        {
            st = mid + 1;
        }
        else
        {
            if(v == 1)
            {
                retine = mid;
                dr = mid - 1;
            }
        }
    }
    cout << '\n' << "! " << retine << '\n';
}