program flip;
var f,g:text;
    v:array[0..17,0..17]of longint;
    n,m,i,j,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 sn:=sn+v[i,j] else sp:=sp+v[i,j];
    sn:=0-sn;
    if (sn>sp)then
      for j:=1 to m do
        v[i,j]:=0-v[i,j];
  end;
for j:=1 to m do
  begin
    sp:=0;
    sn:=0;
    for i:=1 to n do
      if (v[i,j]<0)then sn:=sn+v[i,j] else sp:=sp+v[i,j];
      sn:=0-sn;
      if (sn>sp)then
        for i:=1 to n do
          v[i,j]:=0-v[i,j];
  end;
for i:=1 to n do
  for j:=1 to m do
    s:=s+v[i,j];
writeln(g,s);
close(f);
close(g);
end.