#include <iostream>

using namespace std;

long long n;

int main()
{
    cin>>n;
    int st = 1;
    int dr = n;
    int m, rasp;
    int poz;
    while(st <= dr)
    {
        m = (st + dr) / 2;
        cout<<"? "<<m<<endl;
        cin>>rasp;
        if(rasp == 1)
        {
            dr = m - 1;
            poz = m;
        }
        else if(rasp == 0)
        {
            st = m + 1;
        }
        else
        {
            exit(0);
        }
    }
    cout<<"! "<<poz<<endl;
    return 0;
}