#include <bits/stdc++.h>

using namespace std;
vector<vector<bool>> graph;
int rows, cols, area;

void trace(int r, int c) {
    if (r < 0 || r >= rows || c < 0 || c >= cols) return;
    if (!graph[r][c]) return;
    graph[r][c] = false;
    area++;
    for (int i: {r - 1, r, r + 1}) {
        for (int j: {c - 1, c, c + 1}) {
            trace(i, j);
        }
    }
}

int main() {
    cin >> rows >> cols;
    graph.resize(rows, vector<bool>(cols, false));
    for (int r = 0; r < rows; ++r) {
        for (int c = 0; c < cols; ++c) {
            char connected;
            cin >> connected;
            graph[r][c] = connected == '1';
        }
    }
    int ans = 0;
    for (int r = 0; r < rows; ++r) {
        for (int c = 0; c < cols; ++c) {
            area = 0;
            trace(r, c);
            ans = max(ans, area);
        }
    }
    cout << ans;
}