I'm not accustomed to needing to specify the argument within the code. It's not like it's a command-line flag. I count yours at 78.

while(<>){$a=a;$a++while/$a/i;push@{$_[y///c]},$_ if$a gt f}@_=map$_?@
+$_:(),@_
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If you're to actually print out the shortest, make it 89. Still quite a bit shorter than mine.

while(<>){$a=a;$a++while/$a/i;push@{$_[y///c]},$_ if$a gt f}@_=map$_?@
+$_:(),@_;print$_[0]
[download]

Of course, looking closely only one of your loops needs to be of the 'while' variety. 87 (or 76 unconcerned about output).

for(<>){$a=a;$a++while/$a/i;push@{$_[y///c]},$_ if$a gt f}@_=map$_?@$_
+:(),@_;print$_[0]
[download]

for(<>){$a=a;$a++while/$a/i;push@{$_[y///c]},$_ if$a gt f}@_=map$_?@$_
+:(),@_
[download]