MODULE DIFFERENCE
  IMPLICIT NONE

  CONTAINS

  SUBROUTINE Fdiff(a, n)
    INTEGER, INTENT(IN) :: a(:), n
    INTEGER :: b(SIZE(a))
    INTEGER :: i, j, arraysize

    b = a
    arraysize = SIZE(b)
    DO i = arraysize-1, arraysize-n, -1
      DO j = 1, i
        b(j) = b(j+1) - b(j)
      END DO
    END DO
    WRITE (*,*) b(1:arraysize-n)
  END SUBROUTINE Fdiff
END MODULE DIFFERENCE