namespace AtCoder;

#nullable enable

using System.Numerics;

static class Extensions
{
    public static T[] Repeat<T>(this int time, Func<T> F) => Enumerable.Range(0, time).Select(_ => F()).ToArray();
}

class AtCoder
{
    object? Solve()
    {
        var h = Int();
        var w = Int();
        var a = new int[h + 2, w + 2];
        var d = new Dictionary<int, List<(int, int)>>();
        for (var i = 1; i <= h; i++) for (var j = 1; j <= w; j++)
        {
            var x = Int();
            a[i, j] = x;
            if (d.TryGetValue(x, out var ll)) ll.Add((i, j));
            else d[x] = new List<(int, int)>(){ (i, j) };
        }
        var kz = new List<int>(d.Keys);
        kz.Sort();
        kz.Reverse();
        var ans = 0;
        var g = new int[h + 2, w + 2];
        var moves = new[]{ (-1, 0), (0, -1), (0, 1), (1, 0) };
        foreach (var k in kz)
        {
            var l = d[k];
            foreach (var (i, j) in l)
            {
                var y = 0;
                foreach (var (di, dj) in moves)
                {
                    var ni = i + di;
                    var nj = j + dj;
                    if (a[ni, nj] != a[i, j]) y = Math.Max(y, g[ni, nj] + 1);
                }
                g[i, j] = y;
                ans = Math.Max(ans, y);
            }
        }
        return ans;
    }

    public static void Main() => new AtCoder().Run();
    public void Run()
    {
        var res = Solve();
        if (res != null)
        {
            if (res is bool yes) res = yes ? "Yes" : "No";
            sw.WriteLine(res);
        }
        sw.Flush();
    }

    string[] input = Array.Empty<string>();
    int iter = 0;
    readonly StreamWriter sw = new(Console.OpenStandardOutput()) { AutoFlush = false };

    #pragma warning disable IDE0051
    string String()
    {
        while (iter >= input.Length) (input, iter) = (Console.ReadLine()!.Split(' '), 0);
        return input[iter++];
    }
    T Input<T>() where T : IParsable<T> => T.Parse(String(), null);
    int Int() => Input<int>();
    void Out(object? x, string? separator = null)
    {
        separator ??= Environment.NewLine;
        if (x is System.Collections.IEnumerable obj and not string)
        {
            var firstLine = true;
            foreach (var item in obj)
            {
                if (!firstLine) sw.Write(separator);
                firstLine = false;
                sw.Write(item);
            }
        }
        else sw.Write(x);
        sw.WriteLine();
    }
    #pragma warning restore IDE0051
}