N = int(input())
V = [int(i) for i in input().split()]

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