DFS

        static int DFS(ref int[][] grid, int row, int col, int count, int m)
        {
            if (grid == null || row < 0 || col < 0 || row >= grid.GetLength(0) ||
                col >= m || grid[row][col] == 0)
                return 0;

            grid[row][col] = 0;

            for (int r = row - 1; r <= row + 1; r++)
                for (int c = col - 1; c <= col + 1; c++)
                {
                    count += DFS(ref grid, r, c, 0, m);
                }

            return count + 1;

        }

        static void Main(string[] args)
        {
            int n = Convert.ToInt32(Console.ReadLine());

            int m = Convert.ToInt32(Console.ReadLine());

            int[][] grid = new int[n][];

            for (int i = 0; i < n; i++)
            {
                grid[i] = Array.ConvertAll(Console.ReadLine().Split(' '), gridTemp => Convert.ToInt32(gridTemp));
            }
            int max = 0;
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                {
                    max = Math.Max(DFS(ref grid, i, j, 0, m), max);
                }
            }
            Console.WriteLine(max);

        }