Latex: 6 pictures in two rows aligned horizontally

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\begin{figure}

\centering

\captionsetup[subfigure]{labelformat=empty}%This removes the label from the subfigures

\begin{minipage}{1\linewidth}

\centering

\subfloat[t1]{\label{main:a}\includegraphics[width=3cm]{example-image-a}}

%\stepcounter{figure}\addtocounter{figure}{-1}  %This resets the counter of the subfigures

\subfloat[t2]{\label{main:a}{ }\includegraphics[width=3cm]{example-image-b}}

\subfloat[t\sp{\prime}3]{\label{main:a}{ }\includegraphics[width=3cm]{example-image-c}}

\end{minipage} \par\medskip

\subcaption{(a)} %subcaption

\par\medskip

\vfill %vertical fill

\begin{minipage}{1\linewidth}

\centering

%\stepcounter{figure}\addtocounter{figure}{-1}  %This resets the counter of the subfigures

\subfloat[t1]{\label{main:b}\includegraphics[width=3cm]{example-image-a}}%\par\medskip

\subfloat[t2]{\label{main:b}{ }\includegraphics[width=3cm]{example-image-b}}%\par\medskip

\subfloat[t\sp{\prime}3]{\label{main:b}{ }\includegraphics[width=3cm]{example-image-c}}

\end{minipage}\par\medskip

\subcaption{(b)} %subcaption

\caption{caption}

\label{fig:main}

\end{figure}

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