function migratoryBirds($arr) {
    $typesCount = [];

    foreach ($arr as $type) {
        if (!isset($typesCount[$type])) {
            $typesCount[$type] = 1;
        } else {
            $typesCount[$type]++;
        }
    }

    $maxAmount = max($typesCount);

    $typesWithMaxAmount = array_filter($typesCount, fn ($amount) => $amount === $maxAmount);

    $keys = array_keys($typesWithMaxAmount);

    return min($keys);
}