n = int(input())
v = list(map(int, input().split()))

que = [[0,True]] #[暫定合計値,次回食べていいか否か]
for cnt in range(len(v)):
    now_que1 = []
    now_que2 = []
    for now in que:
        if now[1]:
            now_que1.append([now[0]+v[cnt],False])
            now_que2.append([now[0],True])
        else:
            now_que2.append([now[0],True])
    now_que1.sort(key=lambda x: -x[0])
    now_que2.sort(key=lambda x: -x[0])
    que = []
    que.append(now_que1[0])
    que.append(now_que2[0])
que.sort(key=lambda x: -x[0])
print(que[0][0])