# frozen_string_literal: true

n = gets.chomp.to_i
desks = []
n.times do
  c, d = gets.chomp.split.map(&:to_i)
  desks << [c, d]
end

student = desks.map { |desk| Rational(desk[0], 2).ceil * desk[1] }.sum
max = 1_000_000_000 + 7
puts student % max