
--{-# LANGUAGE StandaloneDeriving #-}
--{-# LANGUAGE BangPatterns #-}

module Main where

import Debug.Trace
--import Data.List
--import Data.Char
--import qualified Data.Set.Strict as Set
--import qualified Data.Map.Strict as Map

main :: IO ()
main = do
  a <- read <$> getLine
  --a `traceShow`
  print $ solve a


solve :: Int -> Int
solve a = sum . map (\x -> let y = a `div` x in x * y * (y + 1) `div` 2) $ [1 .. a]
