#!/usr/bin/perl -l
use strict;
use warnings;
use Getopt::Std;

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

if ($opt_s) {
  print(
      ($ARGV[1] - $ARGV[0] + 1) *
      ($ARGV[0] + $ARGV[1]) / 2
  )
} else {
  print(
      ($ARGV[1] - $ARGV[0]) *
      ($ARGV[0] + $ARGV[1] + 1) / 2
  )
}