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