<?php
$arr = array_map('intval', explode(' ', readline()));
$final = 0;
$first = count($arr) - 1;
if (count($arr) === 1){
    $final = $arr[0];
    echo $final;
    return;
}
for ($i = 0; $i < $first; $i++){
    $modified = [];
    for ($j = 0; $j < $first; $j++){
        $modified[$j] = $arr[$j] + $arr[$j + 1];
    }
    $arr = $modified;
    $final = $arr[0];
}
echo $final;