while(<>){chomp;@_=split/ /,$_;
$i=1;@m=();
while(@_||$i--){
$m[-1]=~/\d/ and $m[-2]=~/\d/ and ($a=pop@m,$b=pop@m,$c=pop@m,(push@m,"$b$a$c"),redo);
push@m,shift@_;
}
print (join" ",(split//,$m[0])); print"\n"
}
Note that non-ascii characters in the above source code will be escaped (such as \x9f).