(Assuming 6 problems in Div2 and 6 problems in Div1 with no subtasks)

How to become Expert: Solve up to D in Div2 or solve up to B in Div1

How to become CM: Keep solving up to D in Div2 or keep solving up to B in Div1

How to become M: Solve E in Div2 or Solve C in Div1

How to become IM: Keep doing the above

How to become GM: Solve F in Div2 or Solve D in Div1

How to become iGM: Keep doing the above

How to become LGM: Solve E in Div1

Sorry for shitposting, but I realized that if I can solve E in Div2 my performance goes from Expert to M which is stupid.

So, if you want to keep gaining rating just wait until you can solve the next problem in a contest.