<?php
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(&$balls): void{
	// １ケもつくれない 
	if(($balls['red'] == 0 or $balls['blue'] == 0) and ($balls['white'] == 0)){
		return;
	}
	
	// 少ない方に全部足してそれが答え
	if(abs($balls['red'] - $balls['blue']) > $balls['white'] ){
		// 宇宙船演算子で比較
		$target = $balls['red'] <=> $balls['blue'];
		
		if($target == 1){
			$target = 'blue';
		}else if($target == -1){
			$target = 'red';
		}else{
			return;
		}

		$balls['violet'] = $balls["$target"] + $balls['white'];
			
		return;
	} 
		
	// 全部足して半分にする
	if(abs($balls['red'] - $balls['blue']) <= $balls['white'] ){
		$violets = ($balls['red'] + $balls['blue'] + $balls['white']) / 2;
		$balls['violet'] = floor($violets);
	}
}