#!/usr/bin/perl
use strict;
use warnings;
use feature qw/ say /;

my $first = ( split ',', <DATA> )[0];

say $first;

__DATA__
1424621700, 2015-02-22 16:15:00, 4294.700
1424621760, 2015-02-22 16:16:00, 4289.700
1424621820, 2015-02-22 16:17:00, 4299.800
1424621880, 2015-02-22 16:18:00, 4302.800
1424621940, 2015-02-22 16:19:00, 4296.900
1424622000, 2015-02-22 16:20:00, 4301.000
1424622060, 2015-02-22 16:21:00, 4300.300


##</code><code>##

$ perl 1140499.pl
1424621700
$