func main()
	var n: int :: cui@input().toInt(&)
	var ss: [][]char :: cui@input().split(" ")
	var a: []int :: #[n]int
	var total: int :: 0
	for i(0, n - 1)
		do a[i] :: ss[2 * i].toInt(&) - ss[2 * i + 1].toInt(&)
		do total :+ a[i]
	end for
	var sum: int :: 0
	
	var ans: int :: -total
	for i(0, n - 1)
		do sum :+ a[i]
		do ans :: [ans, 2 * sum - total].max()
	end for
	
	do cui@print("\{ans}\n")
end func