#ifdef ONPC
#define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<pair<int,int>> vpi;
typedef pair<int,int> pi;
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define popcount __builtin_popcountll
#define forn(i,a,b) for (int i = a; i < b; i++)

void solve(){
    int n,m;cin>>n>>m;
    vvi grid(n,vi(m));
    forn(i,0,n){
        forn(j,0,m){
            cin>>grid[i][j];
        }
    }
    int x=0;
    forn(i,0,n-1){
        forn(j,0,m-1){
            if(grid[i][j]==1&&grid[i][j+1]&&grid[i+1][j+1])x=1;
        }
    }
    if(x==0){
        cout<<0;
        return;
    }
    vvi down(n,vi(m));
    for(int i=n-1;i>=0;i--){
        forn(j,0,m){
            if(grid[i][j]==1){
                down[i][j]=1;
                if(i!=n-1){
                    down[i][j]+=down[i+1][j];
                }
            }
        }
    }
    int ans=0;
    forn(i,0,n){
        forn(j,0,m){
            if(grid[i][j]!=1)continue;
            int curr=1;            
            forn(k,j+1,m){
                if(grid[i][k]!=1)break;
                curr=max(curr,k-j+down[i][k]);
            }
            ans=max(ans,curr);
        }
    }
    cout<<max(0,ans);
    // forn(i,0,n){
        // for(int j=m-1;j>=0;j--){
            
        // }
    // }

}

signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t=1;
    // cin >> t;
    forn(i,0,t){
        solve();
    }
    #ifdef ONPC
    cerr << endl
         << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
    #endif
}