The more exchange transactions you perform, the greater the loss. For each transaction, exchange offices take a commission, sometimes considerable. In this case, it is not always possible to change the currency at a favorable rate.
There is a good service for tracking the best quotes at the moment - BestChange. I personally always use it when I need to change electronic money for rubles or vice versa. The site not only gives the best rate in real time, but also publishes other important information - currency reserves, ratings of exchangers reliability, user reviews.