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

dp = [0] * n
dp[0] = V[0]
dp[1] = max(V[0], V[1])

for i, v in enumerate(V[2:], 2):
    dp[i] = max(dp[i-1], dp[i-2] + v)

print(dp[n-1])