program joculflip;
 var m,n,i,j,s : integer;
    a:array[1..20,1..20] of integer;
    f,g:text;
Begin
 Assign(f,'flip.in');reset(f);
 Assign(g,'flip.out');rewrite(g);
 read(f,n);readln(f,m);
 

for i:= 1 to m do begin
     for j := 1 to n-1 do begin
        read(f,a[i,j]);
     end;
     j:=j+1;
     readln(f,a[i,j]);
     end;
   for i := 1 to  m do begin
      s:=0;
     for j := 1 to n do begin
       s:=s+a[i,j];
     end;
     if (s<-s) then begin
       for j := 1 to n do begin
         a[i,j]:=-a[i,j];
       end;

     end;

   end;
   for j := 1 to n do begin
     s:=0;
     for i := 1 to m do begin
       s:=s+a[i,j];
     end;
     if (s<-s) then begin
      for i := 1 to m do a[i,j]:=-a[i,j];

     end;
   end;
   s:=0;
    for i := 1 to m do begin
      for j := 1 to n do s:=s+a[i,j];
    end;
   write(g,s);
   close(g);close(f);
end.