n = int(input()) L = [0] + list(map(int,input().split())) + [0] D = [] M = 0 for i in range(len(L)): if L[i] == 0: D.append(i) for i in range(len(D)-1): if D[i+1] - D[i] > M: M = D[i+1] - D[i] print(M)