var f,g:text;
    a:array[1..16,1..16] of longint;
    i,j,n,m:byte;
    s:longint;
    ok:boolean;
begin
 assign(f,'flip.in');
 assign(g,'flip.out');
 reset(f);
 rewrite(g);
 read (f,n,m);
 for i:=1 to n do begin
  for j:=1 to m do
   read (f,a[i,j]);
   readln(f);
 end;
 repeat
  ok:=true;
  for i:=1 to n do begin
   s:=0;
   for j:=1 to m do
    s:=s+a[i,j];
   if s<0 then begin
    for j:=1 to m do a[i,j]:=-a[i,j];
    ok:=false;
   end;
  end;
  for j:=1 to m do begin
   s:=0;
   for i:=1 to n do
    s:=s+a[i,j];
   if s<0 then begin
    for i:=1 to n do a[i,j]:=-a[i,j];
    ok:=false;
   end;
  end;
 until ok;
 s:=0;
 for i:=1 to n do
  for j:=1 to m do
   s:=s+a[i,j];
 write(g,s);
 close(f);
 close(g);
end.