#include <iostream>

using namespace std;

int n, x, st, dr, mid;

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