#include < cstdio >
#include < cstring >
using   namespace  std;

int  N,M;
int  Ans;
int  x[ 2510 ][ 2510 ];
int  m[ 2510 ][ 2510 ];
int  f[ 2510 ][ 2510 ];
void  init()
{
     for ( int  i = 1 ;i <= N; ++ i)
         for ( int  j = 1 ;j <= M; ++ j)
            scanf( " %d " , & m[i][j]);
}
int  countx( int  x, int  y)
{
     int  l = 0 ;
     while (x >= 1 && m[x][y] == 0 ){ l ++ ; x -- ; }
     return  l;
}
int  county( int  x, int  y)
{
     int  l = 0 ;
     while (y >= 1 && m[x][y] == 0 ) { l ++ ; y -- ; }
     return  l;    
}
int  countyy( int  x, int  y)
{
     int  l = 0 ;
     while (y <= M && m[x][y] == 0 ) { l ++ ; y ++ ; }
     return  l;
}
int  min( int  x, int  y, int  z)
{
     if (x > y) x = y;  if (x > z) x = z;
     return  x;
}
void  solve()
{
    memset(f, 0 , sizeof (f));
    Ans = 0 ;
     for ( int  i = 1 ;i <= N; ++ i)
         for ( int  j = 1 ;j <= M; ++ j)
             if (m[i][j] == 1 ){
                 int  x = countx(i - 1 ,j),y = county(i,j - 1 );
                f[i][j] = min(x,y,f[i - 1 ][j - 1 ]) + 1 ;
                 if (f[i][j] > Ans) Ans = f[i][j];
            }
    memset(f, 0 , sizeof (f));
     for ( int  i = 1 ;i <= N; ++ i)
         for ( int  j = M;j >= 1 ; -- j)
             if (m[i][j]){
                 int  x = countx(i - 1 ,j),y = countyy(i,j + 1 );
                f[i][j] = min(x,y,f[i - 1 ][j + 1 ]) + 1 ;
                 if (f[i][j] > Ans) Ans = f[i][j];
            }
}
int  main()
{
     while (scanf( " %d%d " , & N, & M) != EOF){
        init();
        solve();
        printf( " %d\n " ,Ans);
    }
     return   0 ;
}