while ($x < $limit) {
  print "Enter P,Q,R: ";
  chomp(my $numbers = <STDIN>);
  my ($p,$q,$r) = split /,/, $numbers;
  
  $x += $p;
  last if $x >= $limit;
  $x *= $q;
  last if $x >= $limit;
  $x /= $r;
}