adding a dot with regular expression in OO

hoping this is in the right place here, if not mods feel free to move

while using search and replace in OO writer i am trying to re-format an E Mini tick file.
the file is in following format

12/7/2010,03:30:00,122275,3
12/7/2010,03:30:00,122300,2
12/7/2010,03:30:01,122275,3
12/7/2010,03:30:02,122300,50

now i need an regex which will place a dot (.) after the 4th digit on the close stamp to retrieve the decimal value like this

12/7/2010,03:30:00,1222.75,3
12/7/2010,03:30:00,1223.00,2
12/7/2010,03:30:01,1222.75,3
12/7/2010,03:30:02,1223.00,50

i guess a regex which will find an 6 digit value between two komma's and then place a dot after the 4th digit ?

hoping for some help as i have no clue how to do this, all help will be appreciated

 

Better to find the number after two commas and divide by 100.

 

found it,

search
,([0-9]{4})([0-9]{2}),
replace
,$1.$2,