program yukicoder2486
  use, intrinsic :: iso_fortran_env
  implicit none
  integer(int64) :: n, diff, ans
  integer(int32) :: m
  integer(int64), allocatable :: arr(:)
  integer(int32) :: i
  read(input_unit, *) n, m
  allocate(arr(m))
  read(input_unit, *) arr(:)
  ans = 0_int64
  do i = 1, m - 1
     diff = arr(i + 1) - arr(i) - 1
     ans = ans + calc_num_last(diff)
  end do
  write(output_unit, '(i0)') ans
contains
  pure recursive integer(int64) function calc_num_last(x) result(res)
    integer(int64), intent(in) :: x
    res = 0_int64; if (x == 0) return
    res = 1_int64; if (x == 1) return
    res = 2_int64; if (x == 2) return
    !> 3 _ _ _ -> _ | _
    !> 5 _ _ _ _ _ -> _ _ | _ _
    if (iand(x, b'1') == 1) then
       res = 2 * calc_num_last(x / 2)
    else !> x is even
       !> 4 _ _ _ _ -> _ | | _
       !> 6 _ _ _ _ _ _ -> _ _ | | _ _
       !> 8 _ _ _ _ _ _ _ _ -> _ _ _ | | _ _ _
       res = x
    end if
  end function calc_num_last
end program yukicoder2486