type matrice=array[1..16,1..16] of integer;
var a:matrice;
    i,s,j,m,n,sn,sp:integer;
    f:text;

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);
  for i:=1 to n do
    begin
      sp:=0;
      sn:=0;
      for j:=1 to m do
        if a[i,j]<0 then inc(sn,abs(a[i,j]))
        else inc(sp,a[i,j]);
      if sp<sn then
        for j:=1 to m do a[i,j]:=-a[i,j];
    end;
  for j:=1 to m do
    begin
      sp:=0;
      sn:=0;
      for i:=1 to n do
        if a[j,i]<0 then inc(sn,abs(a[j,i]))
        else inc(sp,a[j,i]);
      if sp<sn then
        for i:=1 to n do a[j,i]:=-a[j,i];
    end;
  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);
  write(f,s);
  close(f);
end.