      SUBROUTINE FFT(C,N,ISN,IERR)
      DIMENSION C(2)
      IF (IABS(ISN).NE.1) GO TO 10
      CALL SFFT(C,C(2),N,N,N,ISN+ISN,IERR)
      RETURN
   10 IERR=4
      RETURN
      END
