#!/usr/bin/perl -w

use strict;
my $last = "";
my $cursor = -1;
my @output;

while (<DATA>) {
    my ($time, $switch) = split "\t";
    if ($switch eq $last) {
        $output[$cursor] = $_;
    } else {
	   $cursor++;
	   $output[$cursor] = $_;
	   $last = $switch;
    }
}

foreach (@output) {
    print;
}


__DATA__
time1	UP
time2	DOWN
time3	UP
time4	DOWN
time5	DOWN
time6	DOWN
time7	UP
time8	UP
time9	UP
time10	DOWN
time11	UP