A lake near the Arctic Circle is covered by a thick sheet of ice during the cold winter months. When spring arrives, the warm air gradually melts the ice, causing its thickness to decrease at a rate of 0.20.20, point, 2 meters per week. After 777 weeks, the sheet is only 2.42.42, point, 4 meters thick.
Let yyy represent the ice sheet's thickness (in meters) after xxx weeks.