program PrStos;
var
	k : integer;

type stos = ^node;
node=record
	val: integer;
	next: stos;
end;

var
    head: ^node;
	
procedure addstos (x:integer);
var
	pom:^node;
begin
	new(pom);
	pom^.val:=x;
	pom^.next:=head;
	head:=pom;
end;

procedure delstos;
var
   pom:^node;
begin
	if head <>NIL then
	begin
		pom:=head;
		head:= pom^.next;
		dispose(pom);
	end;
end;

procedure show;
var 
	pom:^node;
begin
	pom:=head;
	write('HEAD --> ');
	while (pom<>NIL) do
	begin 
		write(pom^.val, '--> ');
		pom:=pom^.next;
	end;
	writeln ('NIL');
end;

begin
  head :=NIL;
  addstos(5);
  show;
  addstos(15);
  show;
  addstos(25);
  show;
  delstos;
  show;
  readln;
end.