program main
implicit none
integer ::n , m
integer , allocatable :: x(:), y(:)
integer :: i
integer :: a

read(*,*) n,m 
allocate(x(m))
allocate(y(m-1))
read(*,*) x
call heapsort(m,x)
do i = 1, m-1
   y(i) = x(i+1)-x(i)
end do
call heapsort(m-1,y)

a = 0
if( n.ge.m ) then
   a = 0
else
   do i = 1, m-n
      a = a + y(i)
   end do
end if

write(*,'(i0)') a
deallocate(x)
deallocate(y)

stop
contains
subroutine heapsort(n,array)
  implicit none
  integer,intent(in) :: n
  integer,intent(inout) :: array(1:n)
  
  integer ::i,k,j,l
  integer :: t

  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
        end if
     end if
     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
        end if
        if (t.lt.array(j))then
           array(i)=array(j)
           i=j
           j=j+j
        else
           j=k+1
        end if
     end do
     array(i)=t
  end do
 stop
end subroutine heapsort


end program main
