def merge_sort(seq):
    if len(seq) < 2:
        return seq
    mid = len(seq)/2
    front = merge_sort(seq[:mid])
    back = merge_sort(seq[mid:])
    
    ret = []
    while len(front) and len(back):
        if front[0] <= back[0]:
            ret.append(front.pop(0))
        else:
            ret.append(back.pop(0))
    return ret + front + back