Feynman diagrams with feynarts

I'm trying to draw Feynman diagrams with the feynarts.sty package for LaTex. The problem is that if I write the following code:

\begin{feynartspicture}(150,150)(1,1)
\FAProp(0.,10.)(6.,10.)(0.,){/Straight}{0}
\FALabel(3.,9.18)[t]{$1$}
\FAProp(20.,10.)(14.,10.)(0.,){/Straight}{0}
\FALabel(17.,10.82)[b]{$2$}
\FAProp(6.,10.)(14.,10.)(0.8,){/Straight}{0}
\FALabel(10.,5.98)[t]{$3$}
\FAProp(6.,10.)(14.,10.)(-0.8,){/Straight}{0}
\FALabel(10.,14.02)[b]{$4$}
\FAVert(6.,10.){0}
\FAVert(14.,10.){0}
\end{feynartspicture}


I get this:

In practice I get only the label of the propagators but not the propagators. How can I solve this problem?

I solved my own problem. I just need to add

% !TEX TS-program = latex


in the first line of the LaTeX file.