#! ruby
# yukicoder My Practice
# author: Leonardone @ NEETSDKASU

N = gets.to_i

count = 0

N.times do
	ck, dk = gets.split.map(&:to_i)
	ch = (ck >> 1) + (ck & 1)
	count += ch * dk
end

puts count.%(7 + (10**9))