func main()
	var N: int :: cui@input().toInt(&)
	var ans: int :: 0
	const mod: int :: 1000000007
	for(1, N)
		var _: [][]char :: cui@input().split(" ")
		var C: int :: _[0].toInt(&)
		var D: int :: _[1].toInt(&)
		do ans :+ ((C + 1) / 2) % mod * (D % mod)
		do ans :% mod
	end for
	do cui@print("\{ans}\n")
end func