#include <bits/stdc++.h>

using namespace std;

int n, st, dr, poz;

int main() {
    cin >> n;
    st = 1;
    dr = n;
    while(st <= dr) {
        int mij = st + (dr - st) / 2;
        cout << "? " << mij << "\n";
        cout.flush();

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

    return 0;
}