Possible Duplicate:
What is the expression for putting $n$ indistinguishable balls into $k$ indistinguishable cells?
I think that this is quite basic, but I can't seem to get it:
Given $n>0$ identical oranges, and $k \leq n$ identical kids. In how many ways can I divide the oranges between the kids, when every kid gets at least one orange.
Notice that the kids are also identical! I.e it's not two different cases when we switch the amount of oranges between 2 kids.
Thanks!