var i,j,k,r,c,x:longint;

     ch:array[..,..] of char;

     s:string;

     rr,cc:array[..] of boolean;

     pre:array[..] of longint;

 procedure init;

  begin

  readln(r,c);

  for i:= to r do

   begin

    readln(s);

    for j:= to c do ch[i,j]:=s[j];

   end;

  end;

 procedure main;

  begin

  fillchar(rr,sizeof(rr),true);

  fillchar(cc,sizeof(cc),true);

  for x:= to r do

   begin

    pre[]:=;k:=;

    for i:= to c do

     begin

      while (k<>) and (ch[x,k+]<>ch[x,i]) do k:=pre[k];

      if ch[x,k+]=ch[x,i] then inc(k);

      pre[i]:=k;

     end;

    k:=c;

    for i:= to c do

     if c-pre[k]<>i then cc[i]:=false else k:=pre[k];

   end;

  for x:= to c do

   begin

    pre[]:=;k:=;

    for i:= to r do

     begin

      while (k<>) and (ch[k+,x]<>ch[i,x]) do k:=pre[k];

      if ch[k+,x]=ch[i,x] then inc(k);

      pre[i]:=k;

     end;

    k:=r;

    for i:= to r do

     if r-pre[k]<>i then rr[i]:=false else k:=pre[k];

   end;

   for i:= to r do if rr[i] then break;

   for j:= to c do if cc[j] then break;

   writeln(i*j);

   end;

 begin

  init;

  main;

 end.