INT FUNC Fibonacci(INT n)
  INT curr,prev,tmp

  IF n>=-1 AND n<=1 THEN
    RETURN (n)
  FI

  prev=0
  IF n>0 THEN
    curr=1
    DO
      tmp=prev
      prev=curr
      curr==+tmp
      n==-1
    UNTIL n=1
    OD
  ELSE
    curr=-1
    DO
      tmp=prev
      prev=curr
      curr==+tmp
      n==+1
    UNTIL n=-1
    OD
  FI
RETURN (curr)

PROC Main()
  BYTE n
  INT f

  Put(125) ;clear screen

  FOR n=0 TO 22
  DO
    f=Fibonacci(n)
    Position(2,n+1)
    PrintF("Fib(%I)=%I",n,f)

    IF n>0 THEN
      f=Fibonacci(-n)
      Position(21,n+1)
      PrintF("Fib(%I)=%I",-n,f)
    FI
  OD
RETURN