How use "prompt" or something similar for numbers and not for strings ?

Hello, I'm actually using twinery 2, with Harlowe, for the first time, and I have a litle problem ^^'
I want that the user put a number on a variable, so I used the macro "prompt" for do that, but "prompt" give only strings, and not numbers... I don't know how to do for use this with a number...
So, there is an other macro for this, or something to write after or before prompt ?

Thank you for reading and your help, and sorry if I wrote some mistakes, english is not my native language...