//JOI2008予選4
#include<stdio.h>

int check(int x, int y, int count);

int table[92][92];
int m, n, i, j, count = 0;

int main(void)
{
	int max = 0, total;
	
	scanf("%d %d", &m, &n);
	for(i = 0; i < n; i++)
		for(j = 0; j < m; j++)
			scanf("%d", &table[i][j]);
	
	printf("n:%d, m:%d\n", n, m);
	
	for(i = 0; i < n; i++)
		for(j = 0; j < m; j++)
		{
			total = check(i, j, 0);
			printf("(%d, %d)を出発点とした割れる最大値 = %d\n", j, i, total);
			if(total > max) max = total;
		}
	printf("%d\n", max);
	return 0;
}

int check(int x, int y, int count)
{
	int max = 0, tmp;
	if(table[x][y])
	{
		count++;
		table[x][y] = 0;
		if(x < n-1)
			if(max < (tmp = check(x+1, y, count))) max = tmp;
		if(y < m-1)
			if(max < (tmp = check(x, y+1, count))) max = tmp;
		if(x > 0)
			if(max < (tmp = check(x-1, y, count))) max = tmp;
		if(y > 0)
			if(max < (tmp = check(x, y-1, count))) max = tmp;
		
		table[x][y] = 1;
		return max;
	}
	else return count;
}