#! perl -slw
use strict;
use Data::Dump qw[ pp ];

my @data = map[ split ' ' ], <DATA>;
pp \@data;
my @xformed;

push @xformed, [ map shift @$_ // (), @data ] while @{ $data[ 0 ] };

pp \@xformed;

__DATA__
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16