use strict;
my @input = ("A/B/C/D/E/F/", "A/B/C/D/","A/B/C/D","A/B/C/", "A/B/C","A/B","A");
foreach (@input){
  print "$1\n" if m|((?:\w+/){4})|;
}

##</code><code>##

A/B/C/D/
A/B/C/D/

##</code><code>##

A/B/C/D/
A/B/C/D/
A/B/C/D
A/B/C/
A/B/C
A/B
A