def main():
    n = int(input())
    m = list(map(int, input().split()))

    list1 = [0] * n
    list1[0] = m[0]
    if n > 2:
        list1[1] = max(list1[0], m[1])
        for index in range(n - 2):
            list1[index + 2] = max(list1[index] + m[index + 2], list1[index + 1])
        print(max(list1))

    elif n == 1:
        list1[0] = max(list1[0], m[0])
        print(list1[0])
    elif n == 2:
        list1[0] = max(list1[0], m[0])
        print(list1[0])


if __name__ == '__main__':
    main()