let

 proc putmany (n: Integer, c: Char) ~
  let
   var i: Integer
  in
   begin
   i := 0;
   while i < n do
    begin i := i+1; put (c) end
   end;

 var n: Integer;  var r: Integer;
 const mark ~ '@'

in
 begin
 getint (var n); geteol ();
 r := 0;
 while r < (n-1) do
  begin
  r := r + 1;
  putmany (n-r, ' '); put (mark);
  if r >= 2 then
   begin
   putmany (2*r - 3, ' '); put (mark)
   end
  else; !skip
  puteol ()
  end;
 putmany (2*n - 1, mark)
 end