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

DP = [0 for _ in range(n + 2)]
for i in range(n):
    DP[i + 1] = max(DP[i + 1], DP[i])
    DP[i + 2] = max(DP[i + 2], DP[i] + V[i])
print(max(DP[n], DP[n + 1]))