import math, sequtils, strutils, sugar

const
  m = 10 ^ 9 + 7
  k = 5 * 10 ^ 8
let
  n = parseInt readLine stdin
  xs = newSeq.collect:
    for _ in 0 ..< n:
      let
        cd = stdin.readLine.split.map parseInt
        c = cd[0] mod m
      var
        d = cd[1]
        result = 0

      while d > k:
        result += (c + 1) div 2 * k
        result = result mod m
        d -= k
      
      result += (c + 1) div 2 * d
      result mod m

echo (sum xs) mod m