program long(input,output);
var
 a:array[1..200,1..200]of longint;
 f:array[0..200,0..200]of longint;
 i,j:longint;
 n,m,k,l,p:longint;
 ans:longint;

begin
 assign(input,'long.in');
 reset(input);
 readln(n,m);
 for i:=1 to n do
 begin
  for j:=1 to m do read(a[i,j]);
  readln;
 end;
 close(input);

 for i:=1 to n do
  for j:=1 to m do
   f[i,j]:=f[i-1,j]+f[i,j-1]-f[i-1,j-1]+a[i,j];

 for i:=1 to n do
  for j:=1 to m do
  begin
   for k:=0 to i do
    for l:=0 to j do
    begin
     p:=f[i,j]-f[i,l]-f[k,j]+f[k,l];
     if (p>0)and((i-k)*(j-l)>ans) then ans:=(i-k)*(j-l);
    end;
  end;

 assign(output,'long.out');
 rewrite(output);
 writeln(ans);
 close(output);
end.