#include <iostream>

using namespace std;

int N;

int ask(int val)
{
    if (val > N)
        return 0;

    cout << "? " << val << '\n';
    cout.flush();
    int r;
    cin >> r;
    return r;
}

int main()
{
    cin >> N;
    int K = 0, pas = (1 << 30);

    while (pas) {
        if (ask(K + pas)) 
            K += pas;
        pas /= 2;
    }

    cout << "! " << K << '\n';
}