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

dp = [[0, 0] for i in range(N + 1)]

for i, v in enumerate(V, start=1):
    dp[i][0] = max(dp[i - 1][0], dp[i - 1][1])
    dp[i][1] = dp[i - 1][0] + v

print(max(dp[-1]))