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