$(i=FS=_)=$0{for(;i<NF;a[Y-i]=s$++i)for(s=a[y=Y-i];length(s)/2<Y+i;)s=s" " Y++}END{for(;y++<53;)if(p=a[y-i])print p}

Note that non-ascii characters in the above source code will be escaped (such as \x9f).

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