#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int st = 1, dr = n;
    while(st <= dr)
    {
        int mid = (st + dr) / 2, ok;
        if(st == dr)
        {
            cout << "! " << st << "\n";
            return 0;
        }
        cout << "? " << mid;
        cin >> ok;
        if(ok == 0)
            st = mid + 1;
        else
            dr = mid;
    }

    return 0;
}