Adding letter P to Cell
 

I have a spreadsheet that I have to modify every month. This spreadsheet has a field called StudyID that should have a 3 digit numeric code in it. A letter P should be added to any code that has 3 digit numeric code. Example


"509" Should be "P509"
"927" Should be "P927"
"947" Should be "P947"

I want to create a macro code to do this function because I have to repeat this process every month. Thanks for your help