Many people will assume nobody will think about the problem (1 step thinkers). A few people will assume someone will think about the problem who thought about the people who won't think about the problem (2 step thinkers).
I think most 3+ step thinkers will take the problem to it's most logical inclusion (making them n-step thinkers). Why stop arbitrarily at 3 or 4? They've recognized that people who exist who will think other people exist who thought about the problem. At that point they should be able to recognize that this pattern will continue to n. While I am sure there are 3->(n-1) thinkers, they'll be more rare than n-step thinkers, I'd reason.
There are a number of 0 step thinkers who read the question and answered 33 though.
Now I have a question: Is the person who answers 0 smarter than the people who happened to guess the right answer at the proper point of time, even if at the current time (and possibly indefinitely) they got the problem wrong? aka "I only got the answer wrong because other people didn't think hard enough."