Program Flip;
Var f:text;
    n,m,i,j,ff,s:longint;
    a:array[1..20,1..20] of longint;
Begin
  assign(f,'flip.in');
  reset(f);
  readln(f,n,m);
  for i:=1 to n do
     for j:=1 to m do read(f,a[i,j]);
  close(f);
  repeat
   ff:=0;
   for i:=1 to n do
      begin
       s:=0;
       for j:=1 to m do begin s:=s+a[i,j]; end;
       if -1*s>s then begin ff:=1; for j:=1 to m do a[i,j]:=-1*a[i,j]; end;
      end;
   for j:=1 to m do
      begin
       s:=0;
       for i:=1 to n do begin s:=s+a[i,j]; end;
       if -1*s>s then begin ff:=1; for i:=1 to n do a[i,j]:=-1*a[i,j]; end;
      end;
  until(ff=0);
  s:=0;
  for i:=1 to n do
     for j:=1 to m do s:=s+a[i,j];
  assign(f,'flip.out');
  rewrite(f);
  Writeln(f,s);
  close(f);
End.