How to make it so that when entering data in the input, the text in the botton changes?

Question

Bootstrap

How to make it so that when entering data
1) (note: 20) only in the input from, the text in the button changes (from 20 m²)
2) (approx: 20) only in the input before, the text in the button changes (up to 20 m²)
3 ) in both inputs (approx: 20, 40) the text in the button changed (20 - 40 m²)
jsfiddle.net/hwovzbfz/2

Answer 1

input event