import           Data.Char             (isSpace)
import qualified Data.ByteString.Char8 as B
import qualified Data.List             as L

getIL :: IO [Int]
getIL = L.unfoldr f <$> B.getLine
  where
    f s = do
      (n, s') <- B.readInt s
      return (n, B.dropWhile isSpace s')

main :: IO ()
main = do
  n <- readLn :: IO Int
  xs <- getIL
  print $ sum $ map (\(x, y) -> y * x * (n - x + 1)) $ zip [1 .. ] xs