Assuming you do want to do some calculations, Math::BigInt is for you.

use Math::BigInt;

$a = Math::BigInt->new("3000000000000011");
$b = Math::BigInt->new("1233456789012345");
$a += $b;

print "a: $a\n";
[download]

results in :

a: +4233456789012356
[download]

--
Brovnik