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

my $binSize = 20;
my %binTotals;

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

    $binTotals{int(($pos - 1) / $binSize)} += $coverage;
}

printf "%4d %d\n", 20 * (1 + $_), $binTotals{$_} for sort {$a <=> $b} keys %binTotals;

__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