#!/usr/bin/perl
use warnings;
use strict;
use 5.010;

my $total = 0;
while (<DATA>){
    chomp;
    my ($chr, $pos, $coverage) = split /\t/;
    $total += $coverage;   
}
say $total;

#-------------------------
#data format:
#chr positon_on_DNA coverage
__DATA__
chr	1	2
chr	4	2
chr	7	5
chr	22	5
chr	24	6
chr	38	10
chr	44	10
chr	50	20
chr	57	25
chr	60	30
chr	65	30