import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T

main :: IO ()
main = do
  (n  : _) <- map unsafeSignedDecimal . T.words <$> T.getLine :: IO [Int]
  ds <- map unsafeSignedDecimal . T.words <$> T.getLine :: IO [Int]
  let
    x = snd . foldr step (0, 0) $ ds :: Int
    step d (s, t) = (d + s, d * s + t)
  print x

unsafeSignedDecimal :: T.Text -> Int
unsafeSignedDecimal s = case T.signed T.decimal s of
  Right (n, _) -> n
