program flip;
var f,g:text;
    n,m,i,j:byte;
    v:array[1..16,1..16]of longint;
    sp,sn,s:longint;
begin
assign(f,'flip.in');
assign(g,'flip.out');
reset(f);
rewrite(g);
read(f,n,m);
for i:=1 to n do
  for j:=1 to m do
    read(f,v[i,j]);
for i:=1 to n do
  begin
    sp:=0;
    sn:=0;
    for j:=1 to m do
      if (v[i,j]>0)then
        sp:=sp+v[i,j] else
          sn:=sn+v[i,j];
    sn:=sn*(-1);
    if (sn>sp)then
      for j:=1 to m do
        v[i,j]:=v[i,j]*(-1);
  end;
for j:=1 to m do
  begin
    sp:=0;
    sn:=0;
    for i:=1 to n do
      if (v[i,j]>0)then
        sp:=sp+v[i,j] else
          sn:=sn+v[i,j];
    sn:=sn*(-1);
    if (sn>sp)then
      for i:=1 to n do
        v[i,j]:=v[i,j]*(-1);
  end;
for i:=1 to n do
  for j:=1 to m do
    s:=s+v[i,j];
write(g,s);
close(f);
close(g);
end.