#include <iostream>

using namespace std;

int main() {
    int n, st, dr, mijl, rasp, rez;
    
    cin >> n;
    
    st = 0;
    dr = n;
    while (dr-st>=0) {
        mijl = (st+dr)/2;
        cout << "? " << mijl << '\n';
        cout.flush();
        cin >> rasp;
        if (rasp==0) {
            st = mijl+1;
        } else {
            dr = mijl-1;
            rez = mijl;
        }
    }
    cout << "! " << rez <<' \n';
    return 0;
}