IPv6 Global Unicast Configuration

Hi,

I must to configure an IPv6 Global Unicast on the selfIP. From F5 support (https://support.f5.com/csp/article/K15203), this must be done entering the IPv6 netmask in hexadecimal notation... can someone tell me how to translate a simple /64 prefix length in exadecimal notation?

Thanks in advance, best regards