import Control.Applicative
import Text.Printf

main = do
  n <- fmap (read :: String -> Int) . words <$> getLine
  xs <- fmap (fmap (read :: String -> Integer) . words) . lines <$> getContents
  print $ solve xs
  
solve [] = 0
solve ([c,d]:xs) = add (solve xs) (mul ((c+1) `div` 2) d)
  where add x y = (x + y) `mod` m
        mul x y = (x * y) `mod` m
        m = 1000000000 + 7