from enum import IntEnum, auto


# ステート遷移
class E(IntEnum):
    EAT = 0
    NOT_EAT = auto()

    def nexts(self):
        match self:
            case E.EAT: return [E.NOT_EAT]
            case E.NOT_EAT: return [E.EAT, E.NOT_EAT]
        assert False

    def cost(self, x: int) -> int:
        match self:
            case E.EAT: return x
            case E.NOT_EAT: return 0
        assert False


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

dp = [[0] * len(E) for _ in range(N+1)]
for i, v in enumerate(V):
    for fm in E:
        for to in fm.nexts():
            dp[i+1][to] = max(dp[i+1][to], dp[i][fm] + to.cost(v))

ans = max(dp[N])
print(ans)