def merge_sort(sequence):
    """Returns the sequence, sorted in ascending order.
    """
    l, r = 0, len(sequence) - 1
    if l < r:
        mid = ((r + l) // 2) + 1
        left = sequence[l:mid]
        right = sequence[mid:r+1]
        sequence = merge(sequence, merge_sort(left), merge_sort(right))
    return sequence

def merge(sequence, left, right):
    """Merges two sorted sequences into sequence.
    """
    llen, rlen = len(left), len(right)
    a, b = 0, 0
    for i in range(llen + rlen):
        if a < llen:
            if b < rlen:
                if left[a] <= right[b]:
                    sequence[i] = left[a]; a += 1
                else:
                    sequence[i] = right[b]; b += 1
            else:
                sequence[i] = left[a]; a += 1
        else:
            sequence[i] = right[b]; b += 1
    return sequence