#include<iostream>
using namespace std;
int d,s,o,m;
int main()
{
    for(cin>>d,s=1;s<=d;) {
        m=(s+d)>>1,cout<<"? "<<m<<"\n",cout.flush(),cin>>o;
        if(!o)
            s=m+1;
        else
            d=m-1;
    }
    cout<<"! "<<s,cout.flush();
    return 0;
}