$\=$,=$/;
while($n=2*<>){
$_=' 'x--$n;$_="/$_/$_ \\";@_=();
s!  \\!\\!,@_=($_,@_,y!/\\!\\/!r),s!^! !while/ \\/;
s!^/\K *| *(?=\\/)!'_'x$n!e for@_;
print' 'x($n/2+1).'_'x++$n,@_}