Coins of the United States dollar (aside from those of the earlier Continental currency) were first minted in 1792. New coins have been produced annually and they make up a valuable aspect of the United States currency system. Today, circulating coins exist in denominations of 1¢ (i.e. 1 cent or $0.01), 5¢, 10¢, 25¢, 50¢, and $1.00. Also minted are bullion (including gold, silver and platinum) and commemorative coins. All of these are produced by the United States Mint. The coins are then sold to Federal Reserve Banks which in turn are responsible for putting coins into circulation and withdrawing them as demanded by the country's economy. Current coinage Today, four mints operate in the United States producing billions of coins each year. The main mint is the Philadelphia Mint, which produces circulating coinage, mint sets and some commemorative coins. The Denver Mint also produces circulating coinage, mint sets and commemoratives. The San Francisco Mint produces regular and silver proof coinage, and produced circulating coinage until the 1970s. The West Point Mint produces bullion coinage (including proofs). Philadelphia and Denver produce the dies used at all of the mints. The proof and mint sets are manufactured each year and contain examples of all of the year's circulating coins. The producing mint of each coin may be easily identified, as most coins bear a mint mark. The identifying letter of the mint can be found on the front side of most coins, and is often placed near the year. Unmarked coins are issued by the Philadelphia mint. Among marked coins, Philadelphia coins bear a letter P. Denver coins bear a letter D, San Francisco coins bear a letter S, and West Point coins bear a letter W. S and W coins are rarely found in general circulation, although S coins bearing dates prior to the mid-1970s are in circulation. The CC, O, C, and D mint marks were used on gold and silver coins for various periods from the mid-19th century until the early 20th century by temporary mints in Carson City, Nevada; New Orleans, Louisiana; Charlotte, North Carolina; and Dahlonega, Georgia. Most such coins that still exist are now in the hands of collectors and museums. Coins in circulation Remarks The mass and composition of the cent changed to the current copper-plated zinc core in 1982. Both types were minted in 1982 with no distinguishing mark. Cents minted in 1943