<?php

$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$input = array_map('str_split', $input);
$gamma = $epsilon = [];
for ($i = 0; $i < count($input[0]); $i++) {
    $bit = (int) (array_sum($column = array_column($input, $i)) >= ceil(count($column) / 2));
    $gamma[] = $bit;
    $epsilon[] = ~$bit & 1;
}
echo bindec(implode('', $gamma)) * bindec(implode('', $epsilon)).PHP_EOL; //3813416