program main
  implicit none
  integer(16) i, N, ans, p
  read(*, *) N
  ans = 0
  do i = 1,N
    p = N/i
    ans = ans + i * p * (p + 1)
  end do
  ans = ans/2
  !read(*, *) (L(i), i = 1,N)

  write(*, *) ans
end program main
