import strutils, sequtils, math

proc trfm(x: uint|float): auto = (x.int mod (10 ^ 9 + 7)).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
  cnt = cnt.trfm

echo cnt