#include <iostream>

using namespace std;
int a[501][501],b[501][501],c[501][501],d[501][501],n,m,e[501][501],f[501][501],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;
                if(d[i][j]==1)
                {
                    if(e[i][j-1]==1 || a[i][j-1]>1) e[i][j]=1;
                }
        }
    }
}
void construct_b ()
{ int h;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(e[i][j]==1)
            {
                h=a[i][j-1];
                if(b[i][j-1]>h) h=b[i][j-1];
                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)
            {
                if(e[i+1][j]==1) f[i][j]=1;
                if(f[i+1][j]==1) f[i][j]=1;
            }
        }
    }
     for(int i=n;i>=1;i--)
    {
        for(int j=1;j<=m;j++)
        {
            if(f[i][j]==1)
            {
                h=b[i+1][j];
                if(c[i+1][j]>h) h=c[i+1][j];
                c[i][j]=h+1;
                if(h>maxim) maxim=h;
            }
        }
    }

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