The United States of America (USA), more commonly known as the United States (U.S.) or America, is a federal constitutional republic situated mostly in central North America. Its 48 contiguous states and Washington, D.C., the capital district, rests between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to the east and Russia to the west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean such as Puerto Rico.