Message mapping

We are using Graphical/Message mapping here.....

Problem is: I need to truncate the LAST 10 digits of a string. The source can vary in length.

e.g.

Source: 3245678567945

Target would look like: 5678567945

Analysis:

We looked all the functions available in message mapping, but nothing seems to be in this use. I thought of using the "Substring" function available in Message Mapping, but it is going to give me first 10 digits (Left to Right).

Any expert can help please?