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

result = V[0]

def get_best_combination(v, v_list):
    for i in range(len(v_list)):
        if i > 2:
            break
        tmp_result = get_best_combination(v+v_list[i],v_list[i+2:])
        global result
        result = tmp_result if tmp_result > result else result
    return v

get_best_combination(0,V)
print(result)