aker(0, X, _, R):- R is X+1.
aker(1, X, 1, R):- R is X.
aker(2, _, 0, 0).
aker(3, _, 0, 1).
aker(N, _, 0, 2):- N > 3.
aker(N, X, Y, R):- N1 is N-1, Y1 is Y-1, aker(N, X, Y1, R1), 
	aker(N1,R1,X,R).

/* Poziva se sa: aker(N,X,Y,Rezultat).  */