#include <iostream>

using namespace std;
int a[510][510],b[510][510],c[510][510],d[510][510],n,m,maxim; char c1;
void citire ()
{
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            cin>>c1;
            if(c1=='1') d[i][j]=1;
        }
    }
}
void construct_a ()
{
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(d[i][j]==1)
                a[i][j]=a[i-1][j]+1;
        }
    }
}
void construct_b ()
{ int h;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(d[i][j]==1)
            {
                h=a[i][j-1];
                if(b[i][j-1]>h) h=b[i][j-1];
              if(h!=0)  b[i][j]=h+1;
            }
        }
    }
}
void construct_c ()
{
    int h;
     for(int i=n;i>=1;i--)
    {
        for(int j=1;j<=m;j++)
        {
            if(d[i][j]==1)
            {
               h=b[i+1][j];
               if(c[i+1][j]>h) h=c[i+1][j];
            if(h!=0)   c[i][j]=h+1;
               if(h+1>maxim) maxim=h+1;
            }
        }
    }

}
int main()
{
    citire();
    construct_a();
    construct_b();
    construct_c();
    if(maxim==1) maxim=0;
    cout<<maxim;
    return 0;
}