Condtional calculated column

Hi i have 4 columns A,B,C,D
I  need to create new column E That  should be the Combination of C&D  So E = C&D
and one more condition is there if C Column doesn't have any data, if it is blank it should from the B

ABCD

JP	Wellbeing	SDA/WB	Vacuum cleaner
DE	Wellbeing	C&A	Vacuum cleaner
US	Wellbeing	C&A	Accessories
US	Wellbeing	C&A	Vacuum cleaner
US	Wellbeing	All Others	All Others
US	Wellbeing	SDA/WB	Vacuum cleaner
US	Wellbeing	All Others	Vacuum cleaner
US	Taste	C&A	Water Filtration
ES	Wellbeing	C&A	Vacuum cleaner
US	Wellbeing	C&A	Air Purifier
DE	Wellbeing		All Others
BR	Wellbeing		Accessories
DE	Taste	MDA	Hood
BR	Wellbeing	MDA	Refrigerator
BR	Wellbeing	MDA	Home Environment
DE	Taste	MDA	Dishwasher
ES	Taste	C&A	Oven
DE	Taste	MDA	Oven
IT	Wellbeing	SDA/WB	Iron
DE	Care	MDA	Washing & Drying
DE	Care	All Others	Washing & Drying
ES	Wellbeing	All Others	All Others
FR	Taste	MDA	Hob
IT	Taste	MDA	Dishwasher
DE	Care	C&A	Washing & Drying
ES	Care	MDA	Washing & Drying
DE	Taste	MDA	Cooktop
DE	Taste	MDA	Refrigerator
SE	Wellbeing	C&A	Vacuum cleaner
IT	Wellbeing	C&A	Vacuum cleaner
SE	Wellbeing	SDA/WB	Heaters
DE	Taste	MDA	Hob
ES	Taste	C&A	Accessories
DE	Taste	C&A	Coffee Machine
IT	Taste	MDA	Refrigerator
DE	Wellbeing	SDA/WB	Vacuum cleaner
UK	Taste	SDA/WB	Electric Kettle
DE	Taste	C&A	Dishwasher
DE	Wellbeing	All Others	Foot Care
SE	Wellbeing	SDA/WB	Vacuum cleaner
UK	Taste	SDA/WB	Toaster
UK	Taste	SDA/WB	Coffee Machine
UK	Care	MDA	Washing & Drying
ES	Wellbeing	C&A	Air Purifier
DE	Wellbeing	C&A	Iron
DE	Wellbeing	C&A	Coffee Machine
ES	Taste	C&A	Food Processor
DE	Taste	C&A	Food Processor
DE	Care	C&A	Air Cooler
IT	Taste	MDA	Hood
DE	Taste	C&A	Hob
ES	Taste	MDA	Oven
IT	Taste	MDA	Oven
IT	Taste	C&A	Hood
ES	Care	C&A	Washing & Drying
IT	Care	MDA	Washing & Drying
DE	Taste	C&A	Oven
DE	Taste	SDA/WB	Blenders
DE	Wellbeing	SDA/WB	Air Purifier
DE	Wellbeing	SDA/WB	Iron
DE	Taste	SDA/WB	Coffee Machine
DE	Taste	SDA/WB	Electric Kettle
DE	Wellbeing	SDA/WB	Electric Kettle
ES	Taste	SDA/WB	Food Processor
IT	Wellbeing	SDA/WB	Vacuum cleaner
DE	Taste	C&A	Refrigerator
ES	Taste	MDA	Dishwasher
ES	Taste	C&A	Hob
ES	Taste	MDA	Hob
ES	Wellbeing	SDA/WB	Vacuum cleaner
UK	Wellbeing	C&A	Vacuum cleaner
ES	Wellbeing	C&A	Accessories
ES	Wellbeing	C&A	Iron
ES	Taste	SDA/WB	Blenders
DE	Wellbeing	C&A	Air Purifier
UK	Wellbeing	SDA/WB	Vacuum cleaner
SE	Wellbeing	C&A	Air Purifier
UK	Taste	SDA/WB	Blenders
IT	Wellbeing	C&A	Iron
DE	Taste	SDA/WB	Air Fryer
UK	Taste	MDA	Refrigerator
DE	Taste	C&A	Accessories
IT	Taste	C&A	Coffee Machine
DE	Taste	C&A	Blenders
ES	Taste	C&A	Blenders
DE	Taste	SDA/WB	Toaster
ES	Taste	SDA/WB	Toaster
UK	Wellbeing	SDA/WB	Toaster
ES	Wellbeing	SDA/WB	Iron
IT	Taste	All Others	Refrigerator
DE	Care	C&A	Water Jug
DE	Wellbeing	C&A	Water Filtration
DE	Wellbeing	C&A	Water Jug
DE	Wellbeing	C&A	Accessories
UK	Wellbeing	SDA/WB	Air Purifier
ES	Taste	All Others	Oven
ES	Taste	SDA/WB	Oven
ES	Taste	SDA/WB	Coffee Machine
DE	Taste	MDA	Coffee Machine
UK	Wellbeing	SDA/WB	Iron