package main

import (
	"bufio"
	"fmt"
	"math"
	"os"
	"strconv"
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	var a, b, c float64 // 取った、取った後やから取れへん、取れるけど取らへん
	for i := 0; i < n; i++ {
		sc.Scan()
		v, _ := strconv.Atoi(sc.Text())

		// fmt.Println(a, b, c, v)
		larger := math.Max(b, c)
		a, b, c = larger+float64(v), a, larger
	}

	fmt.Println(int(math.Max(a, b)))
}