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

public class Main {
    public static void main(String[] args) throws Exception {
        new Solution().maxTotalFruits();
    }
}

class Solution {

    final int mod = (int) 1e9 + 7, N = (int) 110, M = 200, INF = 0x3f3f3f3f;


    public void maxTotalFruits() throws Exception {
        Read read = new Read();
        int n = read.nextInt();
        int m = read.nextInt();

        int[][] g = new int[n + 10][m + 10];
        int[][] f = new int[n + 10][m + 10];

        for(int i = 1 ; i <= n ; i ++)
            for(int j = 1 ; j <= m ; j++)
                g[i][j] = read.nextInt();

        int ans = 1;
        for(int i = 1 ; i <= n ; i++){
            for(int j = 1 ; j <= m ; j++){
                f[i][j] = 1;
                if(g[i][j] == g[i-1][j] || g[i][j - 1] == g[i][j])continue;
                f[i][j] = Math.min(Math.min(f[i-1][j],f[i][j-1]),f[i-1][j-1]) + 1;
                ans = Math.max(ans,f[i][j]);
            }
        }
        System.out.println(ans);
    }

}

class Read {
    public BufferedReader in;
    public StringTokenizer tok;
    public PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

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

    public boolean hasNext() {
        while (tok == null || !tok.hasMoreTokens())
            try {
                tok = new StringTokenizer(in.readLine());
            } catch (Exception e) {
                return false;
            }
        return true;
    }

    public String next() {
        hasNext();
        return tok.nextToken();
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public Double nextDouble() {
        return Double.parseDouble(next());
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

}