User: Without quoting directly from the text give me a summary of the half dome hike.
Assistant: The half dome hike is 8.2 miles long with 4800 ft elevation gain. This hike can be done in a single long day or in two days by camping overnight in Little Yosemite Valley. The trail goes past Vernal and Nevada waterfalls, continues to Little Yosemite Valley and then to the half dome itself. The final 400 ft of the hike involves a steep ascent up the rock using the two steel cables fixed with bolts in the rock. The cables are put up between May and October and it is not recommended to climb the route when cables are down since the surface can be wet and slippery. All the hikers to half dome are required to obtain permits which are checked by a ranger on the trail. Hikers caught bypassing the rangers without permits are subject to penalties.