program swastika;
var m,n,i,j,sz,mz,t:integer;
    f,g:text;
    mt:array [1..100,1..100] of integer;
 begin
  assign(f,'flip.in'); reset(f);
  assign(g,'flip.out'); rewrite(g);
  read(f,n); readln(f,m);
  for i:=1 to n do
   begin
    sz:=0; mz:=0;
    for j:=1 to m do
     begin
      if j<>m then read(f,mt[i,j]) else readln(f,mt[i,j]);
      if mt[i,j]>0 then mz:=mz+mt[i,j] else sz:=sz+mt[i,j];
     end;
    if sz+mz<0 then
     for j:=1 to m do
      mt[i,j]:=-1*mt[i,j];
   end;
   for j:=1 to m do
    begin
     sz:=0; mz:=0;
     for i:=1 to n do
      if mt[i,j]<0 then sz:=sz+mt[i,j] else mz:=mz+mt[i,j];
     if sz+mz<0 then
      for i:=1 to n do
       mt[i,j]:=-1*mt[i,j];
    end;
  t:=0;
  for i:=1 to n do
   for j:=1 to m do
    t:=mt[i,j]+t;
  writeln(g,t);
  close(g);
 end.