import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe (fromJust)

readInts :: B.ByteString -> [Int]
readInts = map (fst . fromJust . B.readInt) . B.words

getInts :: IO [Int]
getInts = liftM readInts B.getLine
    
main = do
  n <- readLn
  cds <- replicateM n getInts
  let m = 1000000000 + 7
      s = foldr (\[c, d] s -> ((c+1) `div` 2 * d `mod` m + s) `mod` m) 0 cds
   in print s