package main

import (
	"fmt"
)

func main() {
	var n int

	fmt.Scanf("%d", &n)

	vs := make([]int, n)

	for i := 0; i < n; i++ {
		fmt.Scanf("%d", &vs[i])
	}

	dp := make(map[int]int, n)

	for i, v := range vs {
		if i == 0 {
			dp[i] = v
			continue
		}

		vmax := dp[i-1]

		if i == 1 {
			if vmax < v {
				dp[i] = v
			} else {
				dp[i] = vmax
			}

			continue
		}

		for j := i - 2; j >= 0 && j >= i-2-1; j-- {
			vnext := dp[j] + v
			if vnext > vmax {
				vmax = vnext
			}
		}

		dp[i] = vmax
	}

	fmt.Println(dp[n-1])
}