#include <iostream>

using namespace std;

int query(int X) {
    cout << "? " << X << endl;
    int res;
    cin >> res;
    return res;
}

int main()
{
    int N;
    cin >> N;

    int left = 1, right = N;

    while (left <= right) {
        int mid = (left + right) / 2;

        if (query(mid) == 1) right = mid - 1;
        else left = mid + 1;
    }

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