Converting 2/3 digit numbers to 5 digits with text

Hi guys I've spent ages trying to work this out with no joy
Basically I have a list of numbers, and i need to add 1 char to the front of the number and make it into a 5 digit number.

Heres an example

Number------------------- Needs to Look like this
12--------------------- S00012
14--------------------- S00014
15--------------------- S00015
20--------------------- S00020
50--------------------- S00050
100-------------------- S00100
354-------------------- S00354
555-------------------- S00555
666-------------------- S00666

I have over 1000 rows of these numbers that need to be changed so I was hoping that there is some sort of formula that will do this for me, any help would be greatly appreciated

-Andy

P.S sorry for previous wrong post

thats brill thanks very much