import sys

sys.setrecursionlimit(10 ** 8)

input = sys.stdin.readline


def main():
    N = int(input())
    A = [int(x) for x in input().split()]

    ruiseki = [0] * N
    ruiseki2 = [0] * N
    for i, (x, y) in enumerate(zip(A[::2], A[1::2])):
        if i == 0:
            ruiseki[i] = x - y
        else:
            ruiseki[i] = x - y + ruiseki[i - 1]

    for i, (x, y) in enumerate(zip(A[-1::-2], A[-2::-2])):
        if i == 0:
            ruiseki2[N - 1] = x - y
        else:
            ruiseki2[N - 1 - i] = x - y + ruiseki2[N - i]

    ans = -float("inf")

    for i in range(-1, N):
        if i == N - 1:
            ans = max(ans, ruiseki[i])
        elif i == -1:
            ans = max(ans, ruiseki2[0])
        else:
            ans = max(ans, ruiseki[i] + ruiseki2[i + 1])

    print(ans)

    

if __name__ == '__main__':
    main()