def main():
    N = int(input())
    V = tuple(map(int, input().split()))

    if N < 3:
        print(max(V))
        return

    vlen = len(V)
    ans = []
    for i in (0, 1):
        v = V[i]
        while 1:
            if i + 2 < vlen:
                v1 = V[i+2]
            else:
                break
            if i + 3 < vlen:
                v2 = V[i+3]
            else:
                v2 = 0
            if v1 > v2:
                v += v1
                i += 2
            else:
                v += v2
                i += 3
        ans.append(v)

    print(max(ans))

main()