Latex: 6 pictures in two columns aligned vertically

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\begin{figure}

\begin{minipage}{.5\linewidth}
\centering
\subfloat {\label{main:a}\includegraphics[width=6cm]{example-image-a}}\par\medskip
\subfloat {\label{main:a}\includegraphics[width=6cm]{example-image-a}}\par\medskip
\stepcounter{figure}\addtocounter{figure}{-1}  %This resets the counter of the subfigures
\subfloat[]{\label{main:a}\includegraphics[width=6cm]{example-image-a}}
\end{minipage}%
\begin{minipage}{.5\linewidth}
\centering
\subfloat {\label{main:b}\includegraphics[width=6cm]{example-image-b}}\par\medskip
\stepcounter{figure}\addtocounter{figure}{-1}  %This resets the counter of the subfigures
\subfloat {\label{main:b}\includegraphics[width=6cm]{example-image-b}}\par\medskip
\subfloat[]{\label{main:b}\includegraphics[width=6cm]{example-image-b}}

\end{minipage}\par\medskip

\caption{my fig}
\label{fig:main}
\end{figure}
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