Passage: Sheffield is a geographically diverse city. The city nestles in the eastern foothills of the Pennines, and a natural amphitheatre created by several hills and the confluence of five rivers: Don, Sheaf, Rivelin, Loxley and Porter. As such, much of the city is built on hillsides with views into the city centre or out to the countryside. Blake Street, in the S6 postcode area, is the third steepest residential street in England, with a gradient of 16.6°. The city's lowest point is just 29 metres (95 ft) above sea level near Blackburn Meadows, while some parts of the city are at over 500 metres (1,640 ft); the highest point being 548 metres (1,798 ft) at High Stones, near Margery Hill. However, 79% of the housing in the city is between 100 and 200 metres (330 and 660 ft) above sea level.Estimated to contain around 4.5 million trees, Sheffield has more trees per person than any other city in Europe, and according to Sheffield City Council, it is England's greenest city, a claim that was reinforced when it won the 2005 Entente Florale competition. With more than 250 parks, woodlands and gardens, it has over 170 woodlands (covering 10.91 sq mi or 28.3 km2), 78 public parks (covering 7.07 sq mi or 18.3 km2) and 10 public gardens. Added to the 52.0 square miles (134.7 km2) of national park and 4.20 square miles (10.9 km2) of water this means that 61% of the city is greenspace. Despite this, about 64% of Sheffield householders live further than 300 metres (328 yd) from their nearest greenspace, although access is better in less affluent neighbourhoods across the city. Sheffield also has a very wide variety of habitat, comparing favourably with any city in the United Kingdom: urban, parkland and woodland, agricultural and arable land, moors, meadows and freshwater-based habitats. There are six areas within the city that are designated as sites of special scientific interest.The present city boundaries were set in 1974 (with slight modification in 1994), when the former county borough of Sheffield merged with Stocksbridge...

Question: How many parks are there that  the public are welcome to use?
78