#!/usr/bin/perl -T

use strict;
use warnings;
use utf8;
use open qw(:std :utf8);
use Encode qw(encode decode);

sub usage() {
	print STDERR "usage: $0 filename\n";
	exit;
}

unless ($#ARGV == 0) {
	usage();
}

@ARGV = map { decode("UTF-8", $_) } @ARGV;

my $read_f = $ARGV[0] ;

unless (-e $read_f && -s $read_f) {
	usage;
}

my ($num, $pm_10_sum, $pm_25_sum) = (0, 0, 0);

open(IN, "<", $read_f) or die "omg! can't open input file: $read_f";

while (<IN>) {
	chomp;
	my ($x, $a, $b, $pm_25, $q, $r, $s, $pm_10, $z) = split;
	$pm_25_sum += $pm_25; 
	$pm_10_sum += $pm_10; 
	$num++;
}

printf "Avg PM 2.5 level: %.2f µg/m³\t", $pm_25_sum / $num;
printf "Avg PM 10 level: %.2f µg/m³\n", $pm_10_sum / $num;

close(IN);