Math Operations with input data

Question

Hi there
I hope that you all are doing fine.
I want to code a process in my website with html.
the first question for me is how to get 2 data (float input such as C++) from a user of my website, then multiplying it with 2 others (would be an input or a constant)

Answer 1

put 2 <input type="number"> in html page and grab their data like : <input type="number" onchange="alert(document.getElementsByTagName('input')[0].value)" placeholder="input number">

Answer 2

Thanks
that was beautiful