#!perl -lw
# log files with lines prefixed by unix time.
# subtract the first time from all the rest for time elapsed

use IO::Handle;
STDOUT->autoflush(1);

$prod=1;
for(@ARGV){
    $prod*=$_;
}
if(@ARGV==0){
    $prod=60; # minutes
}

while(<STDIN>){
    unless(defined($prev)){
	die unless /^(\S+):/;
	$prev=$1;
	print;
    }else {
	die unless ($t,$rest)=/^(\S+)(:.*)/;
	printf "%.3f%s\n",($t-$prev)/$prod,$rest;
    }
}