Select using Substring + a Join

I have the following:

select Top(5) substring(ParentId, 0, charindex('-',ParentId,1)) as Parent from assets

1. :
2. : 72
3. : 51
4. : 168
5. : 111

and I have:

select Top(5) parentid from assets

which gives:

1. : 56
2. : 72-10672
3. : 51-10610
4. : 168-10658
5. : 111-10624


How would I go about doing a join where I include ALL parentID's which do not have a - ? and where it uses the first select statement to extract the first part of the ParentID?