#!/usr/bin/perl -l

use strict;
use warnings;

use Getopt::Std;

our ($opt_s);
getopts('s');

# get the range boundaries
my $range_start  = ( $opt_s ) ? $ARGV[0] : $ARGV[0] + 1;
my $range_end    = $ARGV[1];

# compute the sum of the range
my $range_length = $range_end - $range_start + 1;
my $range_sum    = ($range_start + $range_end) * $range_length / 2;

print $range_sum;