You can do iteration for 20 times and change the value of the page in the URL in last by incrementing count for every iteration. To get more clarity on it.
Check the below steps for better understanding,
→ Use repeat number of times activity and give the Repeat number of times value as 20 to iterate twenty times. Output of repeat number of times activity is currentitem.
→ Inside of it insert an assign activity and store the web link in a variable called weblink_str
→ Use the http request after the assign activity and pass the variable to the URL
Repeat number of times activity iterates for 20 times and for every iteration the page number change in the weblink and it will get each page data by HTTP Request activity.
Check the below workflow for better understanding,