use strict;

my $level = 0;
while ( my $line = <STDIN> ) {
    chomp $line;
    chomp $line;

    my $indentString = '   ' x $level;

    # If this is a start tag, increment indentation.
    #
    my $secondChar = substr( $line, 1, 1 );
    if ( '?' ne $secondChar ) {
        if ( '/' eq $secondChar ) {
            $level--;
            $level = 0 unless $level > 0;
            $indentString = '   ' x $level;
        } else {
            if (   $line !~ /<\//
                && $line !~ /\/>/ ) {
                $level++;
            }
        }
    }

    # Emit line with current indentation.
    #
    print $indentString . $line . "\n";

}

#<?xml version="1.0" encoding="ISO-8859-1"?>
#<ONIXmessage>
#<header>
#<m174>Pearson Education</m174>