var v:array [1..100,1..100] of longint;
    k,j,x,m,n,sn,sp,s,l:longint;
    f:text;
begin
 assign(f,'filip.in'); reset(f);
 readln(f,m,n);
 for k:= 1 to m do
  for j:= 1 to n do
   begin
    read(f,x);
    v[k,j]:=x;
   end;
 for k:= 1 to m do
  begin
   sp:=0;
   sn:=0;
   for j:= 1 to n do
    if v[k,j]>0 then
     sp:=sp+v[k,j]
    else
     sn:=sn+v[k,j];
    sn:=sn*(-1);
   if sn>sp then
    for l:=1 to n do
     v[k,l]:=v[k,l]*(-1);
  end;
  for k:= 1 to n do
   begin
     sn:=0;
     sp:=0;
    for j:= 1 to m do
     if v[j,k]>0 then
      sp:=sp+v[j,k]
     else
      sn:=sn+v[j,k];
      sn:=sn*(-1);
   if sn>sp then
    for l:=1 to m do
     v[l,k]:=v[l,k]*(-1);
    end;
 for k:= 1 to m do
  for j:= 1to n do
    s:=s+v[k,j];
 close(f);
 writeln(s);
end.