tokens: If they use the d mark in Serbia , obviously there would be essentially the same system that they have in Montenegro and if they had a currency board with a foreign national running the thing , like Bosnia , it would essentially mean that they had a unified system was what they have in Montenegro because with Montenegro , they would still have the d mark as legal tender , but they would also use this new currency board money from Serbia and there would be absolutely no problem , and furthermore , from a regional point of view , you 'd have essentially most of the Balkans in a unified currency zone because Bulgaria has a currency board that 's d mark based .