package main

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

func max(n1 int, n2 int) int {
	if n1 > n2 {
		return n1
	} else {
		return n2
	}
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Scan(); n, _ := strconv.Atoi(sc.Text())

	vs := make([]int, n)
	for i := 0; i < n; i++ {
		sc.Scan(); v, _ := strconv.Atoi(sc.Text())
		vs[i] = v
	}

	dp := make([]int, n)
	if n >= 1 {
		dp[0] = vs[0]
	}
	if n >= 2 {
		dp[1] = vs[1]
	}
	if n >= 3 {
		dp[2] = vs[0] + vs[2]
	}
	if n >= 4 {
		for i := 3; i < n; i++ {
			dp[i] = max(dp[i - 2], dp[i - 3]) + vs[i]
		}
	}

	if n >= 2 {
		fmt.Println(max(dp[n - 1], dp[n - 2]))
	} else {
		fmt.Println(dp[0])
	}
}