I am only allowed to use loops, conditionals, parallel branches and mutex. Cant really figure out the flow between c2 and c3 especially.
My initial idea is sth like this:

Task A
Task B
Task C
While C2
  Task D
  if !C3
     Task B
     Task C
  else
     Task F
end
if C1
   Task E
   Task F

But I am unsure how much sense this makes, the exit in C3 really throws me off