import sys

N = int(input())
V = list(map(int, input().split()))

if N == 1:
    print(V[0])
    sys.exit()

dp = [[ None ] * 2 for _ in range(1001)]
dp[0][0] = 0
dp[0][1] = V[0]
dp[1][0] = V[0]
dp[1][1] = V[1]

for i in range(2, N):
    dp[i][0] = max(dp[i - 1][1], dp[i - 2][1])
    dp[i][1] = max(dp[i - 1][0] + V[i], dp[i - 2][0] + V[i])

print(max(dp[N - 1][0], dp[N - 1][1]))