Edit: I've removed the first part because, as pointed out in the comments, it is superfluous if the maximum is specified.
The maximum possible number of crazy people such that after hearing all the answers you will be able to trace at least one sane person is
Proof of upper bound
Suppose we have $11$ crazy people and we divide the people into consecutive groups of five with the ordering in seven of the groups being "sane, sane, sane, sane, crazy" and the eighth group being "crazy, crazy, crazy, crazy, sane" (in left-to-right order). Then it is logically consistent for the quintet in each group to respond "sane, sane, sane, crazy, sane" in that order.
However, given these responses, we would not know which quintet is where. Therefore we cannot pin down a single sane person because we might pick out the deviant quintet.
This method can be easily generalised to higher numbers.
Hence, the maximum is less than $11$.
Proof of lower bound
If there are, at most, $10$ crazy people then we are guaranteed a string of people with the pattern "sane, sane, sane, crazy" (in left-to-right order) somewhere in the circle and so we are guaranteed that there is at least a row of three people saying "sane, sane, crazy" in response to the question. Consider the consecutive group of people with the longest string of "sane" responses followed by a "crazy" response. Suppose this represents a string of $k$ people (where we know $2<k$).
I claim that the person who says "crazy" at the end of this group is sane.
To prove this, suppose that this person is crazy. Then, inductively we see that the other $k-1$ people preceding this are also crazy. This means that, in the remaining group of $40-k$, there are at most $10-k$ people who are crazy.
However, this means that there must be a string of size longer than $k$ sane people in a row somewhere in the remaining group. This assertion is not immediate but can be verified by checking through the different possible values of $k$.
This means that there is a string of responses of the form "sane, sane, sane,..., sane, crazy" of length greater than $k$, which is a contradiction.