# -*- coding: utf-8 -*-

import math
N = input()
V = map(int, raw_input().split())
dp = [[0 for i in range(2)] for j in range(N)]
# dp[i][j] : i番目まででi皿目を取ったとき(j == 1)，取らなかったとき(j == 0)それぞれの最大値
dp[0][1] = V[0]
dp[0][0] = 0
if N > 1:
    dp[1][1] = V[1]
    dp[1][0] = dp[0][1]
for i in range(2, N):
    dp[i][1] = max(dp[i - 1][0], dp[i - 2][1], dp[i - 2][0]) + V[i]
    dp[i][0] = max(dp[i - 1][0], dp[i - 1][1], dp[i - 2][1], dp[i - 2][0])
print max(dp[N - 1][1], dp[N - 1][0])