import strutils, sequtils, math
const num = 10 ^ 9 + 7

proc trfm(x: uint|float): auto = (x.int mod num).uint

let N = stdin.readLine.parseInt
var C, D, cnt: uint

for i in 0 ..< N:
  (C, D) = stdin.readLine.split.map parseUint
  cnt += (C.int / 2).ceil.trfm * D.trfm

  while cnt >= num.uint:
    cnt -= num.uint

echo cnt