#include <iostream>

using namespace std;

int up[501][501];

int main()
{

    int n,m,Max = 0;
    cin>>n>>m;
    char a;

    int lstLine = 0;
    int S = 0;

    for(int i=1;i<=n;i++)
    {
        lstLine = -1;
        S = 0;
        for(int j = 1; j <=m; j++)
        {
            cin>>a;
            a-='0';
            if(a)
                up[i][j] = up[i-1][j] + 1;

            if(!a)
                lstLine = -1,S = 0;
            else
                if(lstLine == -1)
                {
                    if(up[i][j] >= 2)
                    {
                        lstLine = 1;
                        S = up[i][j];
                    }
                }
                else
                {
                    S++;
                    if(up[i][j] >= 2)
                    {
                        Max = max(Max, S + up[i][j]-1);
                        S = max(S, up[i][j]);
                    }
                }

        }
    }

    cout<<Max<<'\n';



    return 0;
}