I cannot understand the problem. The question is phrased pOorly !

If there is anyone, who can tell me, the question clearly, I am ready to phrase it in a better way.

Use this statements:
1) There are N different food stuffs in the menu but not all of them are at the distribution.
2) The food is cooked from M different food stuffs.
3) The first student eats and he is not poisoned.
4) The first block describes the food stuffs dangerous for the first student,
5) the next K blocks — for the rest ones.

And try to think a little. It's not very hard. ;)

Combination formula can help.