var a:array[1..100,1..100] of integer;
   i,j,n,m,s,s1, k:integer;
   f,g:text;
begin
  assign(g,'flip.in');
  assign(f,'flip.out');
  reset(g);
  readln(g,m,n);
  rewrite(f);

  for j:=1 to m do
  begin
   for i:=1 to n do
   read(g,a[i,j]);
   readln(g);
  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 k:=1 to n do
   a[k,j]:=-a[k,j] ;
   end;
  end;
  s1:=0;
  for i:=1 to n do
  begin
  s:=0;
  for j:=1 to m do
  s:=s+a[i,j];
  if s<0 then s1:=s1-s
         else s1:=s1+s;
  end;

  write(f,s1);
  close(f);
  close(g);
end.