program depot;
type
    trec = record
        x,y: integer;
	g: boolean;
    end;
    tpole = array[1..100000] of trec;
var
    v,p,i: longint;
    pole: tpole;

procedure sort(var pole: tpole);
var i,j: longint;
    w: trec;
begin
    for i := 1 to p-1 do
	for j := 1 to p-i do
	begin
	    if pole[j].x > pole[j+1].x then begin
		w:= pole[j];
		pole[j] := pole[j+1];
		pole[j+1] := w;
	    end else if pole[j].x = pole[j+1].x then begin
		if pole[j].y > pole[j+1].y then begin
			w:= pole[j];
			pole[j] := pole[j+1];
		    pole[j+1] := w;
		end;
	    end;
	end;
end;

procedure sort2(var pole: tpole);
var i,j: longint;
    w: trec;
begin
    for i := 1 to p-1 do
	for j := 1 to p-i do
	begin
	    if pole[j].y > pole[j+1].y then begin
		w:= pole[j];
		pole[j] := pole[j+1];
		pole[j+1] := w;
	    end else if pole[j].y = pole[j+1].y then begin
		if pole[j].x > pole[j+1].x then begin
			w:= pole[j];
			pole[j] := pole[j+1];
		    pole[j+1] := w;
		end;
	    end;
	end;
end;

begin
    while true do begin
	readln(p);
	if p=0 then break;
	for i:=1 to p do readln(pole[i].x, pole[i].y);
	sort(pole);
	v:=0;
	for i:=1 to p div 2 do begin
	    v := v + pole[i*2].y - pole[i*2-1].y;
	end;	
	sort2(pole);
	for i:=1 to p div 2 do begin
	    v := v + pole[i*2].x - pole[i*2-1].x;
	end;
	writeln('The length of the fence will be ',v,' units.');	
    end;
end.