unity - How to avoid "completely" dark shadow using directional light (as Sun) ?

Look at my scene:

Sun is rising and as you can see the scene is realistic; I mean, that what is in shadow is almost completely dark. This is correct, but i would like something less "dark", like an HDR.

These are some parameters i'm using:

This is my unique Light in scene (Sun):

I'm using also a Post-Processing profile with "Eye Adaption" unflagged.

Can you suggest me what i've to change to make my object affected by shadow less.. dark ?

Thanks

Answer

I've solved adding a "minimum" environment light :

Now, i haven't too dark shadow !