#include <iostream>

using namespace std;

int N;

int main()
{
    cin >> N;
    int le = 1, ri = N;
    int best;
    while(le <= ri) {
        int mid = (le + ri) / 2;
        cout << "? " << mid << "\n";
        cout.flush();
        int x;
        cin >> x;
        if(x == 0) {
            le = mid + 1;
        }
        else {
            best = mid;
            ri = mid - 1;
        }
    }
    cout << "! " << best << "\n";
    cout.flush();
    return 0;
}