{-# LANGUAGE BangPatterns #-}

import Control.Monad
import Data.Array.Unboxed
import Data.Bits
import Data.Char
import Data.Coerce
import Data.Function
import Data.Int 
import Data.IORef
import Data.List
import Data.Maybe
import qualified Data.Vector.Unboxed as V
import qualified Data.Vector.Unboxed.Mutable as MV
import qualified Data.ByteString.Char8 as BS

main :: IO ()
main = do
  n <- getInt
  print $ solve n

solve :: Int -> Integer
solve n = foldr ((+) . fromIntegral) 0 [ i * j * (j + 1) `div`2 | i <- [1..n], let j = n `div` i]

-- input

getInt :: IO Int
getInt = readLn

second :: (b -> c) -> (a, b) -> (a, c)
second f (a, b) = (a, f b)

readInt :: BS.ByteString -> Maybe (Int, BS.ByteString)
readInt = fmap (second BS.tail) . BS.readInt

getIntVec :: Int -> IO (V.Vector Int)
getIntVec n = V.unfoldrN n readInt <$> BS.getLine

getIntList :: IO [Int]
getIntList = map (fst . fromJust . BS.readInt) . BS.words <$> BS.getLine

getIntPair :: IO (Int, Int)
getIntPair = do
  v <- getIntVec 2
  return (v V.! 0, v V.! 1)

-- search

bisearch :: (Int -> Bool) -> (Int, Int) -> (Int, Int)
bisearch check = bis
  where
    bis (l, r)
      | l + 1 == r = (l, r)
      | check mid  = bis (mid, r)
      | otherwise  = bis (l, mid)
      where
        mid = l + (r - l) `div` 2