program ccc
implicit none

integer :: n, m, i
integer,allocatable,dimension(:) :: x, y
integer,dimension(1) :: v

read*, n, m
allocate(x(m))
allocate(y(m-1))
read*, x

call heapsort(m,x)
y=0
do i=1,m-1
y(i)=abs(x(i)-x(i+1))
end do

call heapsort(m-1,y)
do i=m-1,m-1-(n-2),-1
y(i)=0
end do

write(*,'(i0)') sum(y)

end program

subroutine heapsort(n,array)
  implicit none
  integer,intent(in) :: n
  integer,intent(inout) :: array(1:n)
 
  integer ::i,k,j,l
  integer :: t
 
  if(n.le.0)then
     write(6,*)"Error, at heapsort"; stop
  endif
  if(n.eq.1)return

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

  return
end subroutine heapsort