:- use_module(contestlib, [writeN/2]).

cross(N) :-
	hor_line(N),
	N1 is N - 1,
	B1 is N1 // 2, 
	Middle is N1 + B1,
	down(N,'*',0,N1),
	down(N,' ',N1,B1),
	blanks(1), blanks(Middle), stars(1), nl,
	up(N,' ',Middle,B1),
	up(N,'*',N1,N1),
	hor_line(N).

hor_line(N) :- stars(N), blanks(N), stars(N), nl.

down(_,_,_,0) :- !.
down(N,Delimiter,Outer,Lines) :-
	write_line(Delimiter,Outer,N),
	Outer1 is Outer + 1,
	Lines1 is Lines - 1,
	down(N,Delimiter,Outer1,Lines1).	

up(_,_,_,0) :- !.
up(N,Delimiter,Outer,Lines) :-
	Outer1 is Outer - 1,
	write_line(Delimiter,Outer1,N),
	Lines1 is Lines - 1,
	up(N,Delimiter,Outer1,Lines1).	

write_line(Delimiter,OuterSpace,N) :-
	write(Delimiter),
	blanks(OuterSpace),
	stars(1), 
	InnerSpace is 3*N - 4 - 2*OuterSpace,
	blanks(InnerSpace), 
	stars(1), 
	blanks(OuterSpace),
	write(Delimiter),
	nl.

blanks(N) :- writeN(N,' ').

stars(N)  :- writeN(N,'*').