//Nông Dân John | THPT Nguyễn Quang Diêu

Var N,M: Integer;
    A: Array[0..1000,0..1000] of byte;
    F: Array[0..1000,0..1000] of integer;
Procedure Enter;
var i,j: Integer;
begin
    Readln(M,N);
    For i:=1 to M do
      begin
        for j:=1 to N do read(A[i,j]);
        readln
      end;
    Fillchar(F, sizeof(F), 0);
end;
Function max(x,y,z: Integer): integer;
begin
    max:=x;
    if y<max then max:=y;
    if z<max then max:=z;
end;
Procedure Process;
var i,j: integer;
begin
    For i:=1 to M do
    For j:=1 to N do
       if (A[i,j]=A[i-1,j])and(A[i,j]=A[i,j-1])and(A[i,j]=A[i-1,j-1]) then
        F[i,j]:=max(F[i-1,j],F[i,j-1],F[i-1,j-1])+1 else F[i,j]:=1;
end;
Procedure Print;
var i,max,j: Integer;
begin
    max:=F[1,1];
    for i:=1 to m do
    for j:=1 to n do
      if F[i,j]>max then max:=F[i,j];
    Write(max);
end;
Begin
    Assign(input, ''); reset(input);
    Assign(output, ''); rewrite(output);
       Enter;
       Process;
       Print;
    Close(input);
    Close(output)
End.