static int[] dc = {-1, 1, 0, 0, -1, -1, 1, 1};

static int[] dr = {0, 0, -1, 1, -1, 1, -1, 1};

static int[][] field;

static int N;

static int M;

static int maxValue = -(int) 1e9;

public static void main(String[] args) throws IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

StringTokenizer st = new StringTokenizer(br.readLine());

N = Integer.parseInt(st.nextToken());

M = Integer.parseInt(st.nextToken());

field = new int[N][M];

for (int i = 0; i < N; i++) {

st = new StringTokenizer(br.readLine());

for (int j = 0; j < M; j++) {

field[i][j] = Integer.parseInt(st.nextToken());

}

}

for (int i = 0; i < N; i++) {

for (int j = 0; j < M; j++) {

if (field[i][j] == 0) {

maxValue=Math.max(maxValue, BFS(i, j, 0));

}

}

}

System.out.println(maxValue);

}

private static int BFS(int i, int j, int dist) {

Deque<int[]> dq = new LinkedList<>();

dq.offer(new int[]{i, j, dist});

int[][] visited = new int[N][M];

visited[i][j] = 1;

while (!dq.isEmpty()) {

int[] now = dq.pollFirst();

int nc = now[0];

int nr = now[1];

int ndist = now[2];

for (int x = 0; x < 8; x++) {

int cc = nc + dc[x];

int cr = nr + dr[x];

if (0 <= cc && cc < N && 0 <= cr && cr < M) {

if (visited[cc][cr] == 0 && field[cc][cr] == 0) {

visited[cc][cr] = 1;

dq.offer(new int[]{cc, cr, ndist + 1});

} else if (visited[cc][cr] == 0 && field[cc][cr] == 1) {

return ndist+1;

}

}

}

}

return -1;

}

}