%flow fg4:
\flowchart{\flowstart\flowmark0
\flowcompute{$F=1$}\flowmark1
\flowinput{$\quad n\quad$}
\flowdecide{}{no}{yes}{$n$ integer}
\flowdecide{$<$}{$=$}{$>$}{$n$ : 0}
\flowcompute{$i=0$}\flowmark2
\flowcompute{$i=i+1;$ $F=F\times i$}
\flowdecide{yes}{}{no}{$i<n$}\flowmark3
\flowdecide{no}{yes}{}{$F<0$}
\flowendmiddlepart
\flowleftpart\flowoutput{$F$}
\flowdecide{no}{yes}{}{quit?}
\flowendmiddlepart\flowrightpart
\flowend\flowendrightpart
\flowleftpart\flowconnect0\flowendleftpart
\flowendleftpart\flowrightpart
\flowoutput{Error message}
\flowrightconnect0\flowendrightpart
\flowendmiddlepart
\flowleftpart\flowconnect2\flowendleftpart
\flowendmiddlepart\flowrightpart
\flowconnect3\flowendrightpart
\flowleftpart\flowconnect1\flowendleftpart
\flowendmiddlepart\flowrightpart
\flowconnect1\flowendrightpart}