How to define macro containing TikZ \coordinate

I am trying to create a macro to calculate the center of a shape. Consider the following code:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\newcommand{\getcellcent}[4]{
\coordinate (#1) at ($1/3*(V#2)+1/3*(V#3)+1/3*V(#4)$);
}
\begin{document}
\begin{tikzpicture}
\coordinate (V1) at (0,0);
\coordinate (V2) at (2,0);
\coordinate (V3) at (1,1);
\getcellcent{C1}{1}{2}{3}
\draw[black] (V1) -- (V2) -- (V3) -- cycle;
\end{tikzpicture}
\end{document}


Here I get the following error message:

Runaway argument?
1/3*V(3)$); \draw [black] (V1) -- (V2) -- (V3) -- cycle; \node [circ\ETC. ! File ended while scanning use of \tikz@cc@parse@factor.  If I change the line with \getcellcent to \coordinate (C1) at ($1/3*(V1)+1/3*(V2)+1/3*(V3)$);  It works fine. What am I missing here? - the brace in V(#4) is wrong, it should be before the "V". – Ulrike Fischer Feb 2 '13 at 11:49 I confirm this, it works with \coordinate (#1) at ($1/3*(V#2)+1/3*(V#3)+1/3*(V#4)\$);. – Stefan Kottwitz Feb 2 '13 at 11:56
@UlrikeFischer You have the eye of a "hawk". Will you post this as an answer to close the question? – Yiannis Lazarides Feb 2 '13 at 12:09
Thank you! I should of course have spotted this mistake myself.. – Håkon Hægland Feb 2 '13 at 12:13
You can also do a similar calculation without the calc library using \coordinate (#1) at (barycentric cs:V#2=1/3,V#3=1/3,V#4=1/3); – percusse Feb 2 '13 at 12:25

the opening brace in V(#4) is wrong, it should be before the "V"