sharepoint foundation – find text in calculated field

All,

i am trying to extract part of a string in a calculated field.
The calculated field is looking in the title field, of an item in the library, for the word “DIS”.
The formula I am using is the following:
=IF(ISNUMBER(FIND("DIS",Title,10)),MID(Title,INT(FIND("DIS"),Title,10)),13),"")

When it finds the word “DIS” I want the code to extract 13 characters. This code is working fine until the title consists of more than one instance of “DIS”. For example when it runs into the word “DISTANCE”.
I tried to get the last instance using RIGHT()
function in the formula because the characters I am looking for are always somewhere at the end of the title. I cant get this to work.
Can anyone help with that?