In the United States, radio and television broadcast stations are assigned unique identifiers known as call signs. Call signs consist of 4 letters. The first is either \(\mathrm{K}\) or \(\mathrm{W}\) (generally speaking, stations with a \(\mathrm{K}\) call sign are west of the Mississippi River and stations with a W call sign are east of the river, though there are several exceptions to this rule); the remaining 3 letters can be anything. How many possible call signs are there under this system?