flexible exchange rate regime or floating exchange rate regime, the central bank does not intervene in the exchange rate dynamics; hence the exchange rate is determined by the market. Theoretically, in this case reserves are not necessary. Other instruments of monetary policy are generally used, such as interest rates in the context of an inflation targeting regime. Milton Friedman was a strong advocate of flexible exchange rates, since he considered that independent monetary (and in some cases fiscal) policy and openness of the capital account are more valuable than a fixed exchange rate. Also, he valued the role of exchange rate as a price. As a matter of fact, he believed that sometimes it could be less painful and thus desirable to adjust only one price (the exchange rate) than the whole set of prices of goods and wages of the economy, that are less flexible. Mixed exchange rate regimes ('dirty floats', target bands or similar variations) may require the use of foreign exchange operations to maintain the targeted exchange rate within the prescribed limits, such as fixed exchange rate regimes. As seen above, there is an intimate relation between exchange rate policy (and hence reserves accumulation) and monetary policy. Foreign exchange operations can be sterilized (have their effect on the money supply negated via other financial transactions) or unsterilized. Non-sterilization will cause an expansion or contraction in the amount of domestic currency in circulation, and hence directly affect inflation and monetary policy. For example, to maintain the same exchange rate if there is increased demand, the central bank can issue more of the domestic currency and purchase foreign currency, which will increase the sum of foreign reserves. Since (if there is no sterilization) the domestic money supply is increasing (money is being 'printed'), this may provoke domestic inflation. Also, some central banks may let the exchange rate appreciate to control inflation, usually by the channel of cheapening tradable goods. Since the amount of foreign reserves available to defend a weak currency (a currency in low demand) is limited, a currency crisis or devaluation could be the end result. For a currency in very high and rising demand, foreign exchange reserves can theoretically be continuously accumulated, if the intervention is sterilized through open market operations to prevent inflation from rising. On the other hand, this is costly, since the sterilization is usually done by public debt instruments (in some countries