Program flip ;
var a: array[1..5,1..3] of longint;
      n,m,i,j,s : longint;
      f1,f2:text;

Begin
     assign(f1, 'flip.in');
     assign(f2, 'flip.out');
     reset(f1);
     readln(f1,n,m);
     for i:=1 to n do
         for j:=1 to m do
             read(f1,a[i,j]);
     close(f1);
     for i:=1 to m do
         Begin
              s:=0;
              for j:=1 to n do
                  s:=s+a[j,i];
              if s<0 then
                 for j:=1 to n do
                     a[j,i]:=a[j,i]*-1;
         end;
     for i:=1 to n do
         Begin
              s:=0;
              for j:=1 to m do
                  s:=s+a[i,j];
              if s<0 then
                 for j:=1 to m do
                     a[i,j]:=a[i,j]*-1;
         end;
     s:=0;
     for i:=1 to n do
         for j:=1 to m do
             s:=s+a[i,j];
     rewrite(f2);
     writeln(f2,s);
     close(f2);
end.