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);
  if (n<16) and (n>0) and (m>0) then
   begin
   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;
 end.