Project Euler 25

PE25.pl

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use bigint;

my ($a, $b, $idx) = (1, 1, 1);
while(1){
    if( length($a) >= 1000 ){
	print $idx,"\n";
	last;
    }
    $b += $a;
    $a = $b - $a;
    $idx++;
}