use Ensure;
use strict;

my ($x,$limit) = (0,100);

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

print "Finally stopped at $x.\n";