use strict;
use warnings;

open(my $in, '<', 'input.txt')
    or die "Cannot open input.txt: $!";

open(my $out, '>', 'output.txt')
    or die "Cannot open output.txt: $!";

while (<$in>) {
    print $out $_ while s/^\s*\S+\s*//;
}
close($out);
close($in);