Change variable name to prevent shadowing
This PR replaces the `input` variable with `input_string` to prevent shadowing caused by the `input()` function. 

Thanks to @LysandreJik for catching it. 
_The documentation is not available anymore as the PR was closed or merged._<|||||>Since the changes are small, I guess it's good to merge but still confirming. <|||||>Yes, one core maintainer approval is enough to merge.