my @fifth =  @arr[ map {$_*5-1} 1..$#arr+4/5 ];

##</code><code>##

my @fifth =  @arr[ map {$_*5-1} 1..($#arr+4)/5 ];

##</code><code>##

my @fifth =  @arr[ map {$_*5-1} 1..($#arr+1)/5 ];