n = gets.to_i
c ,d = [], []
n.times do
  a, b = gets.split.map(&:to_i)
  c << a
  d << b
end
sum = 0
(0...n).each do |i|
  sum += (c[i] / 2.0).ceil * d[i]
  sum %= 1000000007
end
p sum