{-# LANGUAGE ScopedTypeVariables #-}
module Main where
import Data.List
import Control.Monad

readLine :: Read a => IO [a]
readLine = map read . words <$> getLine

main :: IO ()
main = do
    n <- readLn 
    print $ sum [j*(j+1)`div`2*i|i<-[1..n], let j = n `div` i]