//Code by Patcas Csaba

#include <vector>
#include <string> 
#include <set> 
#include <map> 
#include <queue> 
#include <bitset> 
#include <stack>
#include <list>

#include <numeric> 
#include <algorithm> 

#include <cstdio>
#include <fstream>
#include <iostream> 
#include <sstream> 
#include <iomanip>

#include <cctype>
#include <cmath> 
#include <ctime>
#include <cassert>

using namespace std;

#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >

#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REPEAT do{ 
#define UNTIL(x) }while(!(x)); 

#define SZ size()
#define BG begin() 
#define EN end() 
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()

#define IN_FILE "a.in"
#define OUT_FILE "a.out"

int n, m;
VVI a;
VI dp;

int main()
{
	//Read data
	//freopen(IN_FILE, "r", stdin);
	//freopen(OUT_FILE, "w", stdout);
	
  cin >> n >> m;
  a.RS(n + 1, VI(m + 1));

  string s;
  getline(cin, s);
  dp.RS(m + 1);
  int sol = 0;
  FOR(i, 1, n)
  {
    getline(cin, s);
    FOR(j, 1, m)
    {
      a[i][j] = s[j - 1] - '0';
      if (a[i][j] == 0) dp[j] = 0;
      else ++dp[j];
    }
    int l = 0;
    FOR(j, 1, m)
    {
      if (a[i][j] == 0)
      {
        l = 0;
        continue;
      }
      if (l == 0) 
        if (dp[j] > 1) l = dp[j];
        else continue;
      else 
      {
        if (dp[j] > 1)
        {
          sol = max(sol, l + dp[j]);
        }
        l = max(l + 1, dp[j]);
      }
    }
  }
	//Solve

	//Write data
  cout << sol << endl;


	return 0;
}