import queue

N = int(input())
que = queue.deque(list(map(int, input().split())))
point = 0
for i in range(N):
    if len(que) >= 2:
        left = que[0]-que[1]
        right = que[-1]-que[-2]
        if left > right:
            point += left
            que.popleft()
            que.popleft()
        else:
            point += right
            que.pop()
            que.pop()
    elif len(que) == 1:
        point += que[0]
        break
    else:
        break

print(point)