#include <iostream>

using namespace std;

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin>>n;
    int l=1;
    int r=n;
    int mid;
    int response,ans;
    while(l<=r)
    {
        mid=l+(r-l)/2;
        cout<<"? "<<mid<<endl;
        cin>>response;
        if(response==0)
        {
            l=mid+1;
        }
        else if(response==1)
        {
            r=mid-1;
            ans=mid;
        }
        else
        {
            exit(1);
        }
    }

    cout<<"! "<<ans<<endl;

    return 0;



}