<?php
/**
 * Created by PhpStorm.
 * User: emotu
 * Date: 013 13.2.2019 г.
 * Time: 21:23
 */

$array = explode(" ", readline());

if (count($array) == 1){
    echo $array[0];
    return;
}

//$size = count(arr)

for ($i = 0; $i < count($array); $i++) {
    $array = condense($array);
}


$sum = $array[0];
if (count($array) > 1) {
    $sum += $array[1];
}
echo $sum;
//echo $array[1];

function condense($array2)
{
    $condensed = [];
    for ($i = 0; $i < count($array2) -1; $i++) {
        $condensed[$i] = intval($array2[$i] + $array2[$i + 1]);
    }
    return $condensed;
}