Read a value from keyboard and extract from a text file

Question

Hello!

I have a text file (first.txt) stored on my computer that contains different numbers and I have to enter a value from keyboard and then save in another file (second.txt) which value from first file is lower than the value entered from keyboard.

Does anyone knows how to do this?

I searched all over but I didn't get the answer that I needed.

Thank you in advance!