#include <bits/stdc++.h>

using namespace std;

int main() {

    int n, x, st, dr, rasp, r;

    cin >> n;
    st = 1;
    dr = n;
    while (st <= dr) {
        x = (st + dr) / 2;
        cout << "? " << x << endl;
        cin >> rasp;
        if (rasp == 0) {
            st = x + 1;
        }
        else {
            r = x;
            dr = x - 1;
        }
    }
    cout << "! " << r;

    return 0;
}