from collections import deque n=int(input()) res=float("-inf") que=deque([[0,-1]]) total=0 for i,num in enumerate([int(i) for i in input().split()]*2): total+=num while que and i-que[0][1]>n: que.popleft() if que: res=max(res,total-que[0][0]) while que and que[-1][0]>=total: que.pop() que.append([total,i]) print(res)