Mapping question: IDOC to target

I have question related to PI mapping.

Requirement:  If there are n occurrences in source node, there should be n+1 occurrences on the target Node2  where the first occurrence is derived from other node field.

Source

<row1>

          <Value>1</Value> 

</row1>

<row1>

          <Value>2</Value>

</row1>

<row1>

          <Value>3</Value>

</row1>

To

<row>

  <Value>A</Value> 

</row>

<row>

  <Value>1</Value> 

</row>

<row>

  <Value>2</Value>

</row>

<row>

  <Value>3</Value>

</row>

How can achieve this? Hope I'm clear with my question.

Thanks in advance.