program main
   implicit none
   integer(8)::n,k,i
   integer(8),allocatable,dimension(:)::h,turn,dummy
   real(8),allocatable,dimension(:)::abss
   real(8)::heikin
   read(*,*)n,k
   allocate(h(n),abss(n),turn(n))
   read(*,*)h
!   heikin=real(sum(h),8)/size(h)
 !  abss=abs(h-heikin)
   call heapsort2(n,h,turn)
   do i=1,n-k
   enddo
   allocate(dummy(n-k+1))
   do i=1,n-k+1
     dummy(i)=abs(h(i)-h(i+k-1))
   enddo
   write(*,*)minval(dummy)
 !  do i=1,k
  !    dummy(i)=h(turn(i))
   !enddo
   !write(*,*)maxval(dummy)-minval(dummy)
   !write(*,*)dummy
contains
subroutine heapsort2(n,array,turn)
  implicit none
  integer(8),intent(in)::n
  integer(8),intent(out)::turn(1:n)
  integer(8),intent(inout)::array(1:n)
  
  integer::i,k,j,l,m
  double precision::t
  
  if(n.le.0)then
     write(6,*)"Error, at heapsort"; stop
  endif
  if(n.eq.1)return

  do i=1,N
     turn(i)=i
  enddo

  l=n/2+1
  k=n
  do while(k.ne.1)
     if(l.gt.1)then
        l=l-1
        t=array(l)
        m=turn(l)
     else
        t=array(k)
        m=turn(k)
        array(k)=array(1)
        turn(k)=turn(1)
        k=k-1
        if(k.eq.1) then
           array(1)=t
           turn(1)=m
           exit
        endif
     endif
     i=l
     j=l+l
     do while(j.le.k)
        if(j.lt.k)then
           if(array(j).lt.array(j+1))j=j+1
        endif
        if (t.lt.array(j))then
           array(i)=array(j)
           turn(i)=turn(j)
           i=j
           j=j+j
        else
           j=k+1
        endif
     enddo
     array(i)=t
     turn(i)=m
  enddo

  return
end subroutine heapsort2
end program main
