#include <iostream>
using namespace std;

int main(){

    int n;

    cin >> n;

    int st = 1 , dr = n , aux;

    while(st < dr){

        int mij = (st+dr)/2;

        cout << '?' << mij << '\n';

        cout.flush();

        cin >> aux;

        if(aux == 1) dr = mij;
        else st = mij + 1;
    }

    cout << '!' << st;

    return 0;
}