<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

    <xsl:template match="/">
        <xsl:apply-templates select="students/student//id" />
    </xsl:template>
    
    <xsl:template match="id">
        <xsl:value-of select="." />
    </xsl:template>

</xsl:stylesheet>