I am using the following fields
A1=first name B1=last name c1=joint first name d1=joint last name

I need to Concanate A1, A2 AND C1, D1 if there is a name in c1 and d1 into column E1

I need to Concanate A1, A2 ONLY provided there is no value in C1 & D1 into column E1

It should look like this:

John Jones & Shirly Jones if there is a joint name in C1, D1

OTHERWISE it should like this

John Jones

Please advise. Thank you for your help