/*
*/

//#pragma comment(linker, "/STACK:16777216")
#define _CRT_SECURE_NO_WARNINGS

#include <fstream>
#include <iostream>
#include <string>
#include <complex>
#include <math.h>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <stdio.h>
#include <stack>
#include <algorithm>
#include <list>
#include <ctime>
#include <memory.h>
#include <assert.h>

#define y0 sdkfaslhagaklsldk
#define y1 aasdfasdfasdf
#define yn askfhwqriuperikldjk
#define j1 assdgsdgasghsf
#define tm sdfjahlfasfh
#define lr asgasgash
#define norm asdfasdgasdgsd

#define eps 1e-9
#define M_PI 3.141592653589793
#define bs 666013
#define bsize 256

using namespace std;

const int INF = 1e9;
const int N = 100031;

int n, m;
int board[550][550];
int up[550][550];
int ans;
int best_up;

int main(){
	//freopen("fabro.in","r",stdin);
	//freopen("fabro.out","w",stdout);
	//freopen("F:/in.txt", "r", stdin);
	//freopen("F:/output.txt", "w", stdout);
	ios_base::sync_with_stdio(0);
	//cin.tie(0);

	cin >> n >> m;
	string st;
	getline(cin, st);
	for (int i = 1; i <= n; i++)
	{
		string st;
		getline(cin, st);
		for (int j = 1; j <= m; j++)
		{
			if (st[j - 1] == '1')
				board[i][j] = 1;
			else
				board[i][j] = 0;
		}
	}


	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= m; j++)
		{
			up[i][j] = up[i - 1][j] + 1;
			if (board[i][j] == 0)
				up[i][j] = 0;
		}
	}

	for (int i = 1; i <= n; i++)
	{
		int best_up = -100000;

		for (int j = 1; j <= m; j++)
		{
			if (board[i][j] == 0)
			{
				best_up = -100000;
				continue;
			}
			if (up[i][j] > 1)
			{
				ans = max(ans, best_up + up[i][j]);
				best_up = max(best_up + 1, up[i][j]);
			}
			else
				best_up++;
		}
	}

	cout << ans << endl;

	cin.get(); cin.get();
	return 0;
}