program name
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: n,m,i
    integer(int32), allocatable:: x(:),dx(:)

    read*, n,m
    if (n >= m) then
        print'(i0)', 0
        stop
    end if
    allocate(x(m))
    read*, x(:)
    allocate(dx(m-1))
    call merge_sort(x,1,m)
    do i=1,m-1
        dx(i) = x(i+1)-x(i)
    end do
    call merge_sort(dx,1,m-1)
    print'(i0)', sum(dx(1:m-n))

contains
recursive subroutine merge_sort(ar, fst, lst)
    integer(int32),intent(inout):: ar(:)
    integer(int32),intent(in):: fst,lst
    integer(int32):: mdl

    if (lst-fst < 2) then
        if (ar(fst) > ar(lst)) call swap(ar(fst),ar(lst))
        return
    end if

    mdl = (fst+lst)/2
    call merge_sort(ar, fst, mdl)
    call merge_sort(ar, mdl+1, lst)
    call merge_(ar, fst, mdl, lst)
end subroutine

subroutine merge_(ar, fst, mdl, lst)
    integer(int32),intent(inout):: ar(:)
    integer(int32),intent(in):: fst, mdl, lst
    integer(int32),allocatable:: tmp(:)
    integer(int32):: li, ri, ti

    allocate(tmp(lst-fst+1))

    li=fst
    ri=mdl+1   
    ti=1

    do while (li <= mdl .and. ri <= lst)
        if (ar(li) <= ar(ri)) then
            tmp(ti) = ar(li)
            li=li+1
        else
            tmp(ti) = ar(ri)
            ri=ri+1
        end if
        ti=ti+1
    end do

    if (li <= mdl) then
        tmp(ti:) = ar(li:mdl)
    else
        tmp(ti:) = ar(ri:lst)
    end if

    ar(fst:lst) = tmp(:)
    deallocate(tmp)
end subroutine

subroutine swap(x,y)
    integer(int32),intent(inout):: x,y
    integer(int32):: tmp
    tmp = x
    x = y
    y = tmp
end subroutine
end program name