var
  max,s,n,m,i,j,k,l:longint;
  a:array[0..50,0..50,0..50,0..50]of longint;
  g:array[0..200,0..200]of longint;

begin
  assign(input,'long.in'); reset(input);
  assign(output,'long.out'); rewrite(output);
  readln(n,m);
  for i:=1 to n do
   for j:=1 to m do
   read(g[i,j]);
  for i:=1 to n do
   for j:=1 to m do
    for k:=i to n do
     for l:=j to m do
     if (i<>k)or(j<>l) then
     begin
       a[i,j,k,l]:=a[i,j,k-1,l]+a[i,j,k,l-1]+g[k,l]-a[i,j,k-1,l-1];
       s:=(k-i+1)*(l-j+1);
       if a[i,j,k,l]/s>0 then
       begin
         if s>max then max:=s;
       end;
     end;
  writeln(max);
  close(input);
  close(output);
end.