# -*- coding: utf-8 -*-
"""
Spyder Editor

This is a temporary script file.
"""

#f = open("/Users/naoki/Documents/Atcoder/input.txt")
N = int(input())
A = list(map(int, input().split()))
A.insert(0, 0)

select_num = N//2


Dp = [[[-9999 for _ in range(2)] for _ in range(N+1)] for _ in range(N+1)]

for i in range(1,N+1):
    Start = (i-1)//2
    End = (i+1)//2
    
    for j in range(Start,End+1):
        Dp[i][j][0] = max(Dp[i-1][j][1], Dp[i-1][j][0])   
        # [0] in 3rd dimension  not chosen at last num
        # must be transfered from [i-1]
    for j in range(Start,End+1):
        if Dp[i-1][j-1][0] == -9999 and j == 1:
            Dp[i][j][1] = 0 + A[i]
        else:
            Dp[i][j][1] = Dp[i-1][j-1][0]+A[i]

print(max(Dp[-1][select_num][0], Dp[-1][select_num][1]))