#!/usr/local/perl5/bin/perl -w

$n = <STDIN>;
$i = 1;
$j = 1;
$sum = 0;

for($i = 1; $i <= $n; $i ++)
{
    for($j = 1; $j <= $i; $j++)
    {
	$sum=$sum +$j;
    }
}
print "La somme est ".$sum."\n";