from itertools import accumulate


def accum(a: list):
    acc = list(accumulate(a))
    return lambda l, r: acc[r] - (acc[l-1] if l > 0 else 0)


INF = 1 << 60
N = int(input())
A = list(map(int, input().split()))


def f(xs: list[int]) -> list[int]:
    res = []
    for i in range(0, len(xs), 2):
        res.append(xs[i] - xs[i+1])

    return res


lt = accum(f(A))
rt = accum(f(A[::-1])[::-1])

ans = max(lt(0, N-1), rt(0, N-1))
for i in range(N-1):
    ans = max(ans, lt(0, i) + rt(i+1, N-1))

print(ans)