!
      PROGRAM P62
!
!
      IMPLICIT NONE
      INTEGER ::  I,J
!
      INTERFACE
      SUBROUTINE SWAP(I,J)
      IMPLICIT NONE
      INTEGER, INTENT(IN OUT) :: I,J
      END SUBROUTINE SWAP
      END INTERFACE
!
      PRINT *, 'This is Program >> P62  - Subroutine SWAP'
!
!
!     Tell program where data for  READ *  is coming from
      OPEN(UNIT=5, FILE='P62.DAT')      ! UNIT=5 is the default input
!
      READ *,I,J
      PRINT *,I,J
      CALL SWAP(I,J)
      PRINT *,I,J
      STOP
      END PROGRAM P62
!
      SUBROUTINE SWAP(I,J)
!     This routine will interchange any 2 INTEGER numbers
      IMPLICIT NONE
      INTEGER, INTENT(IN OUT) :: I,J
      INTEGER :: K
      K=I
      I=J
      J=K
      RETURN
      END SUBROUTINE SWAP