<?php

$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
$input = array_map(fn($line) => str_split($line), $input);

$o2 = $co2 = $input;

for ($i = 0; $i < count($input[0]); $i++) {
    if (count($o2) > 1) {
        $bit = (int)(array_sum($column = array_column($o2, $i)) >= ceil(count($column) / 2));
        $o2 = array_filter($o2, fn($line) => $line[$i] == $bit);
    }

    if (count($co2) > 1) {
        $bit = (int) (array_sum($column = array_column($co2, $i)) >= ceil(count($column) / 2));
        $co2 = array_filter($co2, fn ($line) => $line[$i] != $bit);
    }
}
echo bindec(implode('', reset($co2))) * bindec(implode('', reset($o2)));