program pie;
var
  fin,fout:text;
  n,i,t0,ans,a,b:longint;
  v1:array[1..1000]of boolean;
  v2:array[1..1000]of boolean;
begin
  assign(fin,'pie.in'); reset(fin);
  assign(fout,'pie.out'); rewrite(fout);
  read(fin,n);
  for i:=1 to 1000 do begin v1[i]:=false; v2[i]:=false; end;
  ans:=0;
  for i:=1 to n do
  begin
    read(fin,a,b);
    t0:=0;
    if v2[a] then begin v2[a]:=false; inc(t0); end;
    if v1[b] then begin v1[b]:=false; inc(t0); end;
    if t0=2 then
    begin
      dec(t0);
      v1[a]:=true;
      v2[a]:=true;
    end;
    inc(ans,t0);
  end;
  writeln(fout,n*2-ans);
  close(fout);
end.