#include <iostream>
#include <string.h>

using namespace std;

int main()
{
    int n;
    cin >> n;

    int *arr = new int[n];

    for (int i = 0; i < n; i++)
        std::cin >> arr[i];

    int zero_count = 0;
    int max_count = 0;

    for (int i = 0; i < n; i++)
    {
        if (arr[i] == 0)
            zero_count++;
        else if (zero_count != 0)
        {
            if (zero_count != 1)
                if (zero_count > max_count)
                    max_count = zero_count;

            zero_count = 0;
        }
    }

    cout << max_count;

    delete []arr;
}