program christmas_eve
  implicit none
  integer              :: n, k, m, sub, i
  integer, allocatable :: h(:)
  read(*,*) n, k
  allocate(h(n))
  m = 1000000001
  do i = 1, n
     read(*,*) h(i)
  end do
  call merge_sort(n,h)
  do i = 1, n-k+1
     sub = h(i+k-1) - h(i)
     if (sub < m) m = sub
  end do
  deallocate(h)
  write(*,'(i0)') m
  stop
contains
  subroutine merge_sort(n,c)
    implicit none
    integer, intent(in)    :: n
    integer, intent(inout) :: c(n)
    integer                :: number, length, i, ubound
    number = n
    length = 1
    do while (number .gt. 1)
       do i = 1, number/2
          ubound = min(2*i*length,n)
          call merge(c(2*(i-1)*length+1:(2*i-1)*length),c((2*i-1)*length+1:ubound))
       end do
       length = 2*length
       number = (number+1)/2
    end do
    return
  end subroutine merge_sort

  subroutine merge(c1,c2)
    implicit none
    integer, intent(inout) :: c1(:), c2(:)
    integer                :: c(size(c1)+size(c2))
    integer                :: i1, i2, n1, n2
    i1 = 1
    i2 = 1
    n1 = size(c1)
    n2 = size(c2)
    do while (i1 .le. n1 .and. i2 .le. n2)
       if (c1(i1) .lt. c2(i2)) then
          c(i1+i2-1) = c1(i1)
          i1 = i1+1
       else
          c(i1+i2-1) = c2(i2)
          i2 = i2+1
       end if
    end do
    if (i1 .le. n1) then
       c(i1+i2-1:n1+n2) = c1(i1:n1)
    else if (i2 .le. n2) then
       c(i1+i2-1:n1+n2) = c2(i2:n2)
    end if
    c1 = c(1:n1)
    c2 = c(n1+1:n1+n2)
    return
  end subroutine merge

  subroutine swap(a,b)
    implicit none
    integer, intent(inout) :: a, b
    integer                :: c
    c = a
    a = b
    b = c
    return
  end subroutine swap
end program christmas_eve