[xsl] [XSLT 1.0] How to get the last number in a string of numbers?

["Costello, Roger L." <costello@xxxxxxxxx>]

Hi Folks,

I have a variable that contains a bunch of numbers:

   <xsl:variable name="numbers">
      generate some numbers
   </xsl:variable>

I want to obtain the last number in $numbers.

For example, this might be the value of $numbers:

   6 23 45 67

I want the last number:

   67

I want the last number fast, i.e., I want it in constant time, not O(n), where
n is the length of the list of numbers.

Plus, I don't want to use any extension functions/elements.

Finally, I want to use only XSLT 1.0

Can it be done? How?

/Roger