Hi! Experts

Am using MS Office 2007

I have a 3 Columns A,B and C in which 'A' contains First Names, 'B' contains Middle and 'C' contains Last names respectively.

But in certain cases "B" will be blank (i.e. Middle names are not there for certain Names)
i would like to replace the 'BLANK' cells in Column "B" to be filled with N/A.

N/A represents that there is no 'Middle name'

Please help me!

Thank you