window_of_col-2     positions(col-2)    sum of col-3 (coverage) based on window
---------------     --------            ---------------
1-20                1,4,7               9
21-40               22,24,38            21 
41-60               44,50,57,60         85
61-80               65                  30

And, I want to print the results as below:
window SUM
20  9
40  21
60  85
80  30


##</code><code>##

#!/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