N = int(input())
M = 500_001
V = list(map(int, input().split()))
dp = [0, V[0], 0]
ans = V[0]
for i in range(2, N+1):
    x = i % 3
    max_v = max(dp[(x-2) % 3]+V[i-1], dp[(x-1) % 3])
    dp[x] = max_v
    ans = max(ans, max_v)
print(ans)