l = input().split()

cur_len_of_1 = 0
prev_len_of_1 = 0
ans = 0
was_zero = 0

for el in l:
    if el == '1':
        cur_len_of_1 += 1
        ans = max(ans, cur_len_of_1 + prev_len_of_1 + was_zero)
    if el == '0':
        prev_len_of_1 = cur_len_of_1
        cur_len_of_1 = 0
        was_zero = 1

ans = max(ans, cur_len_of_1 + prev_len_of_1 + was_zero)
print(ans)