#!/usr/bin/env perl
use strict;
use warnings;
use utf8;
use feature "say";
use Math::Trig;
&ask;
sub ask{
say "What is the radius?";
my $radius= <STDIN>;
chomp ($radius);
if ($radius==0) {
say "circumference= ", $radius;
}
elsif ($radius<0) {
say "Radius should be greater than 0";
&ask;
}
else {
my $a = 2*pi;
my $c = $a * $radius;
say "circumference= ", $c
}
}