#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
/*
int maxOnes(const vector<int>& v) {
    int n = v.size();
    int left = 0;
    int right = 0;
    int ans = 0;
    while (right < n) {
        left = right;
        while (right < n && v[right] == 1) {
            right++;
        }
        ans = max(ans, right - left);
        right++;
    }
    return ans;
}
 */

int maxOnes(const vector<int>& v) {
    size_t n = v.size();
    // n > 0
    vector<size_t> starts;
    vector<size_t> lengths;

    if (v[0] == 1) {
        starts.push_back(0);
    }
    for (size_t i = 1; i < n; ++i) {
        if (v[i - 1] == 0 & v[i] == 1) {
            starts.push_back(i);
        }
    }

    if (starts.size() == 1 && starts[0] == 0 && v[n - 1] == 1) {
        // only ones
        return n - 1;
    }

    if (starts.size() == 0) {
        // only zeros
        return 0;
    }

    for (size_t start : starts) {
        size_t i = start;
        while (i < n && v[i] == 1) {
            i++;
        }
        lengths.push_back(i - start);
    }

    size_t ans = 0;
    for (auto length : lengths) {
        ans = max(ans, length);
    }

    for (size_t i = 0; i < lengths.size() - 1; i++) {
        if (starts[i] + lengths[i] + 1 == starts[i + 1]) {
            ans = max(ans, lengths[i] + lengths[i + 1]);
        }
    }

    return ans;
}
int main() {

    cout << maxOnes({1, 1, 1, 1}) << endl;
    cout << maxOnes({0, 0, 1, 1}) << endl;
    cout << maxOnes({1, 1, 1, 1, 0, 0, 0, 0, 0}) << endl;
    cout << maxOnes({0, 0, 0}) << endl;
    cout << maxOnes({1}) << endl;
    cout << maxOnes({1, 1, 1, 0, 1, 1}) << endl;
    cout << maxOnes({1,1,1,1, 0,0,0,0,0,1,1,1,1,1,1}) << endl;
    cout << maxOnes({1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1}) << endl;
    cout << maxOnes({1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1}) << endl;

    return 0;
}