Digging quarry timelapse Do you love watching cool timelapses of constructions or other massive work done in minutes? Lets make one here.
We will be looking at an excavator digging quarry, making pictures each day to see whole progress. And your task is to show us this process!

Quarry is defined by the width of its first layer.
Excavator is defined by its capability to dig in one day.

Input

Width of quarry. Integer number, always >= 1.
Excavator dig speed. Integer number, always >= 1.  

Output

Progress of digging quarry on each day.
Started with flat untouched ground and finished with completed quarry.

Rules


On the last day there may be less units to dig, than excavator is
capable of. Excessive work won't be used anywhere, so you should just
output fully dug quarry.
All days progress must be present in the output at once. You can't clear or overwrite previous day progress in the output.
Trailing and leading newlines for each day output are acceptable in any reasonable number.
This is code-golf, so make your code as compact as possible.


Clarifications

Work starts with a flat ground. Length of displayed ground is width of quarry + 2. So there always will be one underscore character on both sides of quarry.

__________


Dug quarry is looking like this for even width:

_        _      
 \      /
  \    /
   \  /
    \/


And like this for odd width

_       _      
 \     /
  \   /
   \ /
    V


Here are examples of quarry progress:

_ _______
 V          dug 1 unit

_  ______
 \/         dug 2 units

_     ___
 \___/      dug 5 units


_       _
 \   __/    dug 10 units
  \_/


Full progress example. Quarry width: 8. Excavator speed: 4 units per day.

__________

_    _____
 \__/

_        _
 \______/

_        _
 \    __/
  \__/

_        _
 \      /
  \  __/
   \/

_        _
 \      /
  \    /
   \  /
    \/


Cornercases

Excavator will need to dig on the last day exactly its capability (speed)

Width: 7, Speed: 3
Width: 10, Speed: 4
Retina 0.8.2, 163 156 bytes

.+
$*_
(_+)¶(_+)
$2¶$1¶$1
r`__\G
$%`$&amp;
¶
;
(?&lt;=(_+);.*)(?&lt;=;_+;\1*)_
¶$`_
m`^_+;
__
+`(&gt;*)_(_+)(_+&lt;?;)\2
$1_$.2$* $3¶$1&gt;$2&lt;;
T`&gt;\_` \\`&gt;+_
T`\\\_;&lt;`V/_`.&lt;|;


Try it online! Explanation:

.+
$*_


Convert the inputs to unary. This gives us W¶S.

(_+)¶(_+)
$2¶$1¶$1


Swap the inputs and duplicate the width. This gives us S¶W¶W.

r`__\G
$%`$&amp;


Calculate the volume of the quarry. This gives us S¶W¶V.

¶
;


Join the inputs into one line. This gives us S;W;V.

(?&lt;=(_+);.*)(?&lt;=;_+;\1*)_
¶$`_


Calculate the amount of progress for each day on its own line. Each day has the format S;W;D, where D is 0 on the first line and increments by S each day until it reaches V.

m`^_+;
__


Delete S and increase W by 2 on each line. This gives us G;D for each day.

+`(&gt;*)_(_+)(_+&lt;?;)\2
$1_$.2$* $3¶$1&gt;$2&lt;;


While D is nonzero, dig either D or G-2 from the line (so the first and last characters are always left), moving the depth to the next line. Each line is indented with one more &gt; than the previous. Newly dug lines also include a &lt;.

T`&gt;\_` \\`&gt;+_


Turn the indent into spaces and the following _ into a \.

T`\\\_;&lt;`V/_`.&lt;|;


If a &lt; is following a \ then turn it into a V, if it's following a _ then turn it into a /. Delete all the &lt;s and ;s.