srand(1);  # So everything is using the same numbers
my $s = 0;
for (1..1000000) {
  $s += nearest_sqrt(int(rand(2**47)));
}
print "$s\n";

##</code><code>##

use ntheory qw/divisors/;
sub closest {
  my @d = divisors(shift);
  $d[ $#d >> 1 ];
}

##</code><code>##

use ntheory qw/fordivisors/;
sub closest {
  my($n,$sqrtn,$min) = ($_[0], int(sqrt($_[0])));
  fordivisors { $min = $_ if $_ <= $sqrtn; } $n;
  $min;
}

##</code><code>##

use ntheory qw/factor/;
sub closest {
  my($n) = @_;
  my(@factors, @d, @t);
  # 1. Get list of factors
  @factors = factor($n);
  # 2. Turn this into an unsorted list of divisors
  @d = (1);
  while (my $p = shift @factors) {
    my $e = 1;
    while (@factors && $p == $factors[0]) { $e++; shift(@factors); }
    push @d,  @t = map { $_ * $p } @d;               # multiply through once
    push @d,  @t = map { $_ * $p } @t   for 2 .. $e; # repeat
  }
  # 3. Sort
  @d = sort {$a<=>$b} @d;
  # 4. Return the largest divisor <= sqrt n.
  $d[ $#d >> 1 ];
}

##</code><code>##

use Math::Pari qw/divisors/;
sub closest {
  my $d = divisors(shift);
  $d->[ $#$d >> 1 ];
}

##</code><code>##

use Math::Factor::XS qw/factors/;
sub closest {
  my @d = (1, factors($_[0]), $_[0]);
  $d[ $#d >> 1 ];
}