n = int(input()) p = [0] + list(map(int, input().split())) d = [0] * (n+1) d[1] = p[1] for i in range(2, n+1): k = 0 ans = 0 while True: if k == i + 1: break ans = max(ans, p[k] + d[i-k]) k += 1 d[i] = ans print(d[n])