#! perl -slw
use strict;

my @data;
while( <DATA> ) {
    if( /^\s/ ) {
        push @{ $data[ -1 ] }, split;
    }
    else {
        push @data, [ split ];
    }
}

print "@$_" for sort{
    substr( $a->[ 3 ], -1 ) cmp substr( $b->[ 3 ], -1 )
}@data;

__DATA__
a1q   b1w   c1e   d1r   e1t   f1y
a2u   b2i   c2o   d2p   e2a   f2s
a3d   b3f   c3g   d3h   e3j   f3k
   p3   q3   r3
   s3   t3   u3
a4l   b4z   c4x   d4c   e4v   f4b
a5n   b5m   c5q   d5w   e5e   f5r
   p5   q5   r5
   s5   t5   u5
a6t   b6y   c6u   d6i   e6o   f6p