package main

import "fmt"

var direction = [][]int{{0, 1}, {0, -1}, {1, 0}, {-1, 0}}

func main() {
	var M, N int
	fmt.Scanln(&N, &M)
	sea := make([][]int, N)
	visited := make([][]bool, N)
	for i := 0; i < N; i++ {
		sea[i] = make([]int, M)
		visited[i] = make([]bool, M)
	}

	for i := 0; i < N; i++ {
		for j := 0; j < M; j++ {
			fmt.Scan(&sea[i][j])
		}
	}
	// 开始遍历sea
	result := 0
	for i := 0; i < N; i++ {
		for j := 0; j < M; j++ {
			if sea[i][j] == 1 && !visited[i][j] {
				area := bfs(i, j, &sea, &visited)
				if area>result{
				    result = area
				}
			}
		}
	}

	fmt.Println(result)
}

func bfs(i, j int, sea *[][]int, visited *[][]bool) int {
	queue := make([][2]int, 0)
	queue = append(queue, [2]int{i, j})
	(*visited)[i][j] = true
	area := 0
	for len(queue) != 0 {
		pos := queue[0]
		for i := 0; i < 4; i++ {
			newX := pos[0] + direction[i][0]
			newY := pos[1] + direction[i][1]
			if newX < 0 || newX >= len(*sea) || newY < 0 || newY >= len((*sea)[0]) {
				continue
			}
			if (*sea)[newX][newY] == 1 && !(*visited)[newX][newY] {
				queue = append(queue, [2]int{newX, newY})
				(*visited)[newX][newY] = true
			}
		}
		queue = queue[1:]
		area += 1
	}
	return area
}