cau4

def unname(first,afterx):
    # '78' vs '7889':
    # => first = '7', afterx = '89'
    first = int(first)
    for y in afterx:
        if int(y) > first:
            return True
        if int(y) < first:
            return False
    return False

def compare(a,b):
    if a == b:
        return False
    a = str(a)
    b = str(b)
    _lena = len(a)
    _lenb = len(b)
    x = min(_lena, _lenb)
    if int(a[:x]) > int(b[:x]):
        return True
    if int(a[:x]) < int(b[:x]):
        return False

    if _lena > _lenb:
        return not unname(a[0],a[x:])
    return not unname(b[0],b[x:])

def custom_sort(arr):
    for i in range(len(arr) -1):
        for j in range(i, len(arr)):
            if not compare(arr[i],arr[j]):
                a = arr[i]
                arr[i] = arr[j]
                arr[j] = a
    return ''.join(str(e) for e in arr)

custom_sort([40, 1, 99, 12])