#include <bits/stdc++.h>

using namespace std;

int n, st, dr, poz;

int main() {
    cin >> n;
    st = 0;
    dr = n;
    while(st <= dr) {
        int mij = st + (dr - st) / 2;
        cout << "? " << mij << endl;
        cout.flush();

        int x;
        cin >> x;
        if(x == 0) {
            poz = mij;
            st = mij + 1;
        }
        else dr = mij - 1;
    }
    cout << "! " << poz << endl;
    cout.flush();

    return 0;
}