#include <iostream>
using namespace std;
int N;
int main()
{
    cin>>N;

    int p1,p2,pmijl,k;
    k=0;
    p1=1;
    p2=N;

    while(p1<=p2)
    {
        pmijl=(p1+p2)/2;

        cout<< "? " << pmijl << "\n";
        cout.flush();

        int c;
        cin>>c;

        if(c==1)
        {
            k=pmijl;
            p1=pmijl+1;
        }

        if(c==0)
        {
            p2=pmijl-1;
        }

        if(c==-1)
        {
            return 0;
        }
    }

    cout<< "! " << k << "\n";
    cout.flush();

    return 0;
}