Sum up the value

I have the following XML file. How do I code in my XSL
to get the sum of value from Field3? Thanks


<?xml version="1.0" encoding="UTF-8" ?> 
<range>
<row>
  <field label="item" name="item" table="D1"
type="number">1</field> 
  <field label="Field3" name="Field3" table="D1"
type="number">42676</field> 
  </row>
<row>
  <field label="item" name="item" table="D1"
type="number">2</field> 
  <field label="Field3" name="Field3" table="D1"
type="number">105813446</field> 
</row>
</range>


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