I just checked and I see the option to use an existing email address (in Russia). It's available in the account creation form, as an option below the field that

I just checked and I see the option to use an existing email address (in Russia). It's available in the account creation form, as an option below the field that asks you what you want your GMail-address to be. Might be A/B-testing though and you're in a group that doesn't have it available at the moment.