object Main {
  def main(args: Array[String]) {
    val sc = new java.util.Scanner(System.in)
    val n = sc.nextInt

    val mod = 1e9.toInt + 7
    var ans = 0L
    for (i <- 0 to n-1) {
      val c, d = sc.nextLong
      // println(c, d)

      // c 個の椅子がある机に座れる人数
      val n = (c / 2) + (c % 2)
      ans = (ans + (n % mod) * (d % mod)) % mod
    }
    println(ans)
  }
}