#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int st=1,dr=n;
    int ans;
    while(st<=dr){
        int mid=(st+dr)/2;
        cout<<"? "<<mid<<'\n';
        int t;
        cin>>t;
        if(t==0) st=mid+1;
        else if(t==1){
            dr=mid-1;
            ans=mid;
        }
        else return 0;
    }
    cout<<"! "<<ans<<'\n';
    return 0;
}