Fixing bug in demo-practicum

In Problem 3 of the While Lops section the 1-st and the 3-rd
environments were in conflict to each other, fixing the 3-rd one.
Some spelling fixes of word "закрашенны".
Some cosmetic commentaries fixes.
8 jobs for master in 4 minutes and 32 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #15505
linux
build:linux

00:01:26

passed #15504
mac_old
build:mac

00:02:03

passed #15503
win32
build:win32

00:01:07

passed #15502
winxp
build:winxp

00:01:42

 
  Dist
passed #15509
linux
dist:linux

00:00:16

passed #15508
mac_old
dist:mac

00:01:40

passed #15507
win32
dist:win32

00:00:16

passed #15506
winxp
dist:winxp

00:00:14