func main()
	var n: int :: cui@inputInt()
	var ans: int :: 0
	const mod: int :: 1000000007
	for(1, n)
		var c: int :: cui@inputInt()
		var d: int :: cui@inputInt()
		do ans :+ ((c + 1) / 2) % mod * (d % mod)
		do ans :% mod
	end for
	do cui@print("\{ans}\n")
end func