In both your programs you have:

while ($k>=2)
    {
    if ($k==1)     
        {last;}
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so the condition for entering the while loop is $k>=2 but inside the loop itself someone might guess that you're checking if $k==1 and it may not become clear that there's a decrement towards the while block end, for readability and logic flow it would be better if this is written down towards the end of the while block after $k=$k-1; for example, but again, since you don't want $k==1 to be considered the loop would exit automatically if you only write while($k>2) without the need to check if $k has reached to 1.

compare:

while($k>2){
        $k=$k-1;
        print "$k\n";
        }
#and
while($k>=2){
        $k=$k-1;
        #last if $k==1;
        print "$k\n";
        }
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$total=0; is used only once, what is it intended to contain?, where @first is coming from in  $ntotal+=$_ for @first;
Another major point, using strictures can save you a lot of nasty repercussions arising from undiscovered bugs and for readability you may want to pick up an indentation that is intuitive or use Perltidy, here is an initial tutorial.