! 簡単なサブルーチンの例
PROGRAM main

  IMPLICIT NONE
  INTEGER :: i, j, k

  READ *, i, j, k
  IF ( i < j ) CALL swap( i, j )
  IF ( j < k ) CALL swap( j, k )
  IF ( i < j ) CALL swap( i, j )
  PRINT *, i, j, k

END PROGRAM main

! swapping
SUBROUTINE swap( p, q )

  IMPLICIT NONE
  INTEGER :: p, q, r

  r = p
  p = q
  q = r

END SUBROUTINE swap