program flip;
var f,g:text; n,m,i,j:integer; A:array[1..16,1..16] of integer; found:boolean;
S:integer;
procedure citire;
begin
Readln(f,n,m);
For i:=1 to n do
 begin
 For j:=1 to m do
  Read(f,A[i,j]);
 Readln(f);
 end;
end;
begin
Assign(f,'flip.in'); Reset(f);
Assign(g,'flip.out');Rewrite(g);
citire; Close(f);
Repeat
found:=false;
For i:=1 to n do
 begin
 S:=0;
 For j:=1 to m do S:=S+A[i,j];
 If S<0 then
  begin
  For j:=1 to m do A[i,j]:=-A[i,j];
  found:=true;
  end;
 end;
For j:=1 to m do
 begin
 S:=0;
 For i:=1 to n do S:=S+A[i,j];
 If S<0 then
  begin
  For i:=1 to n do A[i,j]:=-A[i,j];
  found:=true;
  end;
 end;
Until not found;
S:=0;
For i:=1 to n do
 For j:=1 to m do
  S:=S+A[i,j];
Write(g,S); Close(g);
end.