We recommend that you change about 30-35€ for the first day in Russia. That should be an sufficient amount to get by for one day. You might need some cash to buy lunch since cards are not always accepted. When in Russia you can change the rest of your euros as the rate is usually better there. Our Tour Leaders will provide the best info on exchange rates and best places to do so.
Looking for a currency converter? Here is one with up to date information and even some tips for traveling.