* Line 1: An integer K giving the number of entries in FJ's list that
could be the extra number (or, K=0 means that there is no
number on the list whose removal yields a feasible pairing of
friends).
* Lines 2..1+K: Each line contains the index (1..N+1) within the input
ordering of a number of FJ's list that could potentially be
the extra number -- that is, a number that can be removed such
that the remaining N numbers admit a feasible set of
friendships among the cows. These lines should be in sorted
order.
Removal of the first number in FJ's list (the number 1) gives a remaining
list of 2,2,1,3, which does lead to a feasible friendship pairing -- for
example, if we name the cows A..D, then the pairings (A,B), (A,C), (A,D),
and (B,C) suffice, since A has 3 friends, B and C have 2 friends, and D has
1 friend. Similarly, removing the other "1" from FJ's list also works, and
so does removing the "3" from FJ's list. Removal of either "2" from FJ's
list does not work -- we can see this by the fact that the sum of the
remaining numbers is odd, which clearly prohibits us from finding a
feasible pairing.