#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

while (<STDIN>) {
    print;
    /^B (\S+)/ && read_input($1);
}

sub read_input {
    my ($file) = @_;

    open my $fh, '<', $file;

    while (<$fh>) {
        print;
        /^B (\S+)/ && read_input($1);
    }

    close $fh;

    return;
}