How to grab a number from inside a .html file using regex

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Hello guys! Need your precious help again!

In every html file i have in the very first line a page_id fro counetr
countign purpsoes like in a format of a comment like this:

<!-- 1 -->
<!-- 2 -->
<!-- 3 -->

and so on. every html file has its one page_id

How can i grab that string representaion of a number from inside
the .html file using regex and convert it to an integer value?

# ==============================
# open current html template and get the page ID number
# ==============================

f = open( '/home/webville/public_html/' + page )

 #read first line of the file
firstline = f.readline()

page_id = re.match( '<!-- \d -->', firstline )
print ( page_id )