<?php
// 連想配列で処理
list($r, $b, $w) = explode(" ", trim(fgets(STDIN)));

$balls = array(
	'red' => $r,
	'blue' => $b,
	'white' => $w,
	'violet' => 0
);

makeViolet($balls);

echo $balls['violet'];


function makeViolet(&$balls): void{
	$violets = ($balls['red'] + $balls['blue'] + $balls['white']) / 2;
	$balls['violet'] = floor($violets);
}