Dynamic interface determination

Hi,

I am doing one scenario where I need to determine interface dynamically. So I have created 2 message mappings and 2 Interface mappings in IR. Where as in interface determination in ID, I am using these 2 interfaces mapping with condition where I need to check substring from input1.

<?xml version="1.0" encoding="UTF-8"?>

<ns0:MT_test xmlns:ns0="urn:aa-bb:test">

<Input>

<Input>

<Input1>1234567890</Input1>

</Input>

</Input>

</ns0:MT_test>

Condition:

/p1:MT_test/Input/Input/[(substring('Input1',4,2) = "45")]

For this I already referred dynamic-interface-determination-based-on-file-cont and other web bogs and xPath functions but till I am not able to get any answer.