sub f{
#23456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123456789_123
%h=@_;$h{$_}||=[]for map@$_,values%h;for(@k=keys%h){for$x(@k){push@{$h{$x}},@{$h{$_}}for@{$h{$x}}}}sort{-1+2*grep$_ eq$b,@{$h{$a}}}@k
}