program main
  implicit none
  integer::N,M,minimum,i,j
  integer,allocatable::D(:),DD(:)
  read *,N,M
  allocate(D(M),DD(M))
  read *,D
  DD = qsort(D)
  minimum = 30000

  do i=1,M-N+1
     j = i+N-1
     if(D(i)*D(j).ge.0) then
        minimum = MIN(minimum, MAX(ABS(D(i)),ABS(D(j))))
     else
        minimum = MIN(minimum, ABS(D(i))+ABS(D(j)) + MIN(ABS(D(i)),ABS(D(j))))
     end if
  end do

  print '(i0)',minimum
contains
  recursive function qsort(x) result(y)
    integer,intent(in) ::x(:)
    integer,allocatable::y(:)
    integer::pivot,total
    total = size(x)
    if (total <=1) then
       y = x
    else
       pivot = x(total/2)
       y = [qsort(pack(x, x .lt. pivot)), &
            pack(x, x .eq. pivot),        &
            qsort(pack(x, x .gt. pivot))]
    endif
  end function qsort
end program main