/*
:- export demo/0.

demo :- 
        write('Enter N : '), read(N), nl, 
        fib(N, Fib), 
        write('Fib of '), write(N), write(' is '), writeln(Fib).
*/
fib(0, 1).
fib(1, 1).
fib(N, X) :-
	 N > 1,
	 N2 is N-2,
	 fib(N2, X2),
	 N1 is N-1,
	 fib(N1, X1),
	 X is X1+X2.