\documentclass{article}
        \usepackage{pdfpages} % for \includepdf[pages=-]

        \begin{document}
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\includepdf[pages={2,4}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={5,7}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={6,8}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={9,11}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={10,12}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={13,15}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={14,16}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={17,19}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={18,20}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={21,23}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={22,24}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={25,27}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={26,28}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={29,31}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={30,32}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={33,35}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={34,36}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={37,39}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={38,40}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={41,43}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={42,44}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={45,47}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={46,48}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={49,51}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={50,52}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={53,54}, nup=1x2,landscape=false]{combine.pdf}
\includepdf[pages={54,54}, nup=1x2,landscape=false]{combine.pdf}

        \end{document}