Need help with If statements loop through entire work book rows pasting values

Hi All,

I need a code that will run through each row in the workbook, and for column E i would like the row to equal this...
If there is a value in column D for that row, paste it in column E.... Else If, go check column C for a value and paste it in column E.... Else If, (both contain no value) put the string "N/A"

How would I write a code for this Sample.xlsm

Anything would help, cheers