Mapping doubt

Hi Experts,

My source data will have below structure.

<Source>
<D_235>Type</D_235>
<D_234>Number</D_234>
<D_235_2>Type</D_235_2>
<D_234_2>Number</D_234_2>
<D_235_3>Type</D_235_3>
<D_234_3>Number</D_234_3>

</Source>

Target Structure:

<Target>

<IDTNR>

</Target>

Mapping condition is:

IDTNR will contain concatenation of all Numbers which are coming from source if Type is not equals to "VN"

Data may come from source in any format like:

With only one number

<D_235>

<D_234>

<D_235_2>Type</D_235_2>

<D_234_2>Number</D_234_2>

<D_235_3/>

<D_234_3/>

or with two numbers

<D_235>A</D_235>

<D_234>123</D_234>

<D_235_2>B</D_235_2>

<D_234_2>876</D_234_2>

<D_235_3/>

<D_234_3/>

or with all 3 numbers with one type as "VN"

<D_235>H</D_235>

<D_234>980</D_234>

<D_235_2>P</D_235_2>

<D_234_2>760</D_234_2>

<D_235_3>VN</D_235_3>

<D_234_3>435</D_234_3>

Please help me on mapping for IDTNR field.

Thanks & Regards,

A.Neelima.