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

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