def count_and_update(s):
    s_list = list(s)
    count = 0

    for i in range(len(s_list)):
        if s_list[i] == '0':
            if (i >= 1 and s_list[i - 1] == '0') or (i >= 2 and s_list[i - 2] == '0'):
                count += 1
                s_list[i] = '1'  # 条件に合ったら '1' に変更

    updated_s = ''.join(s_list)
    return count, updated_s

n = int(input())
s = input().strip()

count, updated_s = count_and_update(s)

print(count)