package main

import (
	"fmt"
	"math"
)

func main() {
	var n, a int
	_, _ = fmt.Scan(&n)

	nums := make([]int, n)
	for i := range nums {
		_, _ = fmt.Scan(&a)
		nums[i] = a
	}

	// fmt.Println(nums)

	// 皿を取ることで得られる利益
	gains := make(map[int]int, 0)
	for i := 0; i < n; i++ {
		gains[i] = nums[i]
		if i != n-1 {
			gains[i] -= nums[i+1]
		}
		if i != 0 {
			gains[i] -= nums[i-1]
		}
	}

	// fmt.Println(gains)

	ans := 0
	for n > 0 {
		max := math.MinInt64
		maxI := -1

		for i := 0; i < len(nums); i++ {
			if a, ok := gains[i]; ok {
				if maxI < 0 || max < a {
					maxI = i
					max = a
				}
			}
		}

		if maxI != len(nums)-1 {
			if _, ok := gains[maxI+1]; ok {
				if _, ok := gains[maxI+2]; ok {
					gains[maxI+2] += nums[maxI+1]
				}
				n--
				delete(gains, maxI+1)
			}
		}
		if maxI != 0 {
			if _, ok := gains[maxI-1]; ok {
				if _, ok := gains[maxI-2]; ok {
					gains[maxI-2] += nums[maxI-1]
				}
				n--
				delete(gains, maxI-1)
			}
		}

		ans += nums[maxI]
		delete(gains, maxI)
		n--
		// fmt.Println(maxI, max, nums[maxI], ans, gains)
	}

	fmt.Println(ans)
}