program swastika;
var f,g:text;
    m,n,mz,sz,i,j,count:integer;
    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
   for j:=1 to m do
    if j<>m then read(f,mt[i,j]) else readln(f,mt[i,j]);
  for i:=1 to n do
   begin
    mz:=0; sz:=0;
    for j:=1 to m do
     if mt[i,j]>0 then mz:=mz+mt[i,j] else sz:=sz+mt[i,j];
    if mz+sz<0 then
     for j:=1 to m do
      mt[i,j]:=-1*mt[i,j]
   end;
  for i:=1 to m do
   begin
    mz:=0; sz:=0;
    for j:=1 to n do
     if mt[j,i]>0 then mz:=mz+mt[j,i] else sz:=sz+mt[j,i];
    if mz+sz<0 then
     for j:=1 to n do
      mt[j,i]:=-1*mt[j,i];
   end;
  count:=0;
  for i:=1 to n do
   for j:=1 to m do
    count:=count+mt[i,j];
  writeln(count);
 end.