import Data.Functor
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe
import Debug.Trace

countExaminee :: [[Int]] -> Int
countExaminee (_:xs) = cir (count xs)
  where
    cir = (`mod` 1000000007)
    count :: [[Int]] -> Int
    count [] = 0
    count ((c:d:_):xs) = v' + (cir (count xs))
      where
        c' = cir c
        d' = cir d
        v' = cir (((c' + 1) `div` 2) * d')

readInts :: B.ByteString -> [Int]
readInts s = fst <$> mapMaybe (B.readInt) (B.words s)

main :: IO ()
main = countExaminee <$> (readInts <$>) <$> B.lines <$> B.getContents >>= putStrLn . show