BugLife#1-C

import java.util.*;
import java.io.*;
import java.math.*;

public class Main
{
    public static void process(int test_number)throws IOException
    {
        int n = ni(), m = ni();
        int dp[][][] = new int[n + 1][m + 1][4 + 1], arr[][] = new int[n + 1][m + 1], res = 0;

        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= m; j++){
                arr[i][j] = ni();
                dp[i][j][arr[i][j]] = 1;
            }

        for(int i = 1; i <= n; i++){
            for(int j = 1; j <= m; j++){
                int num = arr[i][j];
                dp[i][j][num] += Math.min(dp[i - 1][j][num], Math.min(dp[i][j - 1][num], dp[i - 1][j - 1][num]));
                res = Math.max(res, dp[i][j][num]);
            }
        }

        p(res + "\n");
    }

    static final long mod = (long)1e9+7l;
    static boolean DEBUG = true;
    static FastReader sc;
    static PrintWriter out;
    public static void main(String[]args)throws IOException
    {
        out = new PrintWriter(System.out);
        sc = new FastReader();

        long s = System.currentTimeMillis();
        int t = 1;
        // t = ni();
        for(int i = 1; i <= t; i++)
            process(i);

        out.flush();
        System.err.println(System.currentTimeMillis()-s+"ms");
    }

    static void trace(Object... o){ if(!DEBUG) return; System.err.println(Arrays.deepToString(o)); };
    static void pn(Object o){ out.println(o); }
    static void p(Object o){ out.print(o); }
    static int ni()throws IOException{ return Integer.parseInt(sc.next()); }
    static long nl()throws IOException{ return Long.parseLong(sc.next()); }
    static double nd()throws IOException{ return Double.parseDouble(sc.next()); }
    static String nln()throws IOException{ return sc.nextLine(); }
    static long gcd(long a, long b){ return (b==0)?a:gcd(b,a%b);}
    static int gcd(int a, int b){ return (b==0)?a:gcd(b,a%b); }

    static class FastReader{
        BufferedReader br;
        StringTokenizer st;

        public FastReader(){
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next(){
            while (st == null || !st.hasMoreElements()){
                try{ st = new StringTokenizer(br.readLine()); } catch (IOException  e){ e.printStackTrace(); }
            }
            return st.nextToken();
        }

        String nextLine(){
            String str = "";
            try{ str = br.readLine(); } catch (IOException e) { e.printStackTrace(); }
            return str;
        }
    }
}