package main

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

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func max(list []int) int {
	maxNum := 0
	for _, n := range list {
		if n > maxNum {
			maxNum = n
		}
	}
	return maxNum
}

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

	n := nextInt(sc)
	dp := make([]int, n)
	for i := 0; i < n; i++ {
		sumV := nextInt(sc)
		if i == 2 {
			sumV += dp[0]
		} else if i > 2 {
			sumV += max(dp[i-3 : i-1])
		}
		dp[i] = sumV
	}

	start := max([]int{0, n - 2})
	fmt.Println(max(dp[start:]))
}