\begin{scope}[node distance=0.75cm]

\node (DoDo4) [inner xsep=0.01cm, inner ysep=0.03cm] at (0, 0) {@};

\node (TimesAp)
  [xshift=0.25cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=DoDo4, left of=DoDo4]
  {@};

\node (Times)
  [xshift=0.25cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=TimesAp, left of=TimesAp]
  {$+$};

\node (Do4) 
  [xshift=-0.5cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=DoDo4,
  right of=DoDo4, yshift=-0.5cm]
  {@};

\node (Do_2)
  [xshift=0.25cm, inner xsep=0.04cm, inner ysep=0.05cm, below of=Do4, left of=Do4, xshift=2]
  {double};

\node (4)
  [xshift=-0.25cm, inner xsep=0.01cm, inner ysep=0.03cm, below of=Do4, right of=Do4, xshift=-2]
  {4};

\draw[->] (DoDo4) to (TimesAp);
\draw[->] (TimesAp) to (Times);
\draw[->] (TimesAp) |- (Do4);
\draw[->] (DoDo4) to (Do4);
\draw[->] (Do4)  to (Do_2);
\draw[->] (Do4)  to (4);

\end{scope}