I've created an `IObservable<>` combination using `CombineLatest()`:

```
IObservable<IList<List<TileItem>>> combination = Observable.CombineLatest(combinations);

```

I need:

```
1. to do something `doSomethingOnFirst()` when first element is reached.
2. to do something `doSomethingOnComplete()` when subscription has completed.

```

Up to now, I've been able to do something when combination is completed. Nevertheless, I don't quite figure out what do I need to do in order to do something when subscription starts...

```
combination
    .Subscribe(
        _ => { },
        _ => { },
        () => this.doSomethingOnCompleted()
    );

```

Any ideas?