Early evidence for proto-Chinese millet agriculture is Radiocarbon dating to about 7000 BC. The earliest evidence of cultivated rice, found by the Yangtze River, is carbon-dated to 8,000 years ago. Farming gave rise to the Jiahu culture (7000 to 5800 BC). At Damaidi in Ningxia, 3,172 Neolithic signs in China dating to 6000–5000 BC have been discovered, "featuring 8,453 individual characters such as the sun, moon, stars, gods and scenes of hunting or grazing". These pictographs are reputed to be similar to the earliest characters confirmed to be written Chinese. Chinese proto-writing existed in Jiahu around 7000 BC, Dadiwan culture from 5800 BC to 5400 BC, Damaidi around 6000 BC and Banpo dating from the 5th millennium BC. Some scholars have suggested that Jiahu symbols (7th millennium BC) were the earliest Chinese writing system. Excavation of a Peiligang culture site in Xinzheng county, Henan, found a community that flourished in 5,500 to 4,900 BC, with evidence of agriculture, constructed buildings, pottery, and burial of the dead. With agriculture came increased population, the ability to store and redistribute crops, and the potential to support specialist craftsmen and administrators. In late Neolithic times, the Yellow River valley began to establish itself as a center of Yangshao culture (5000 BC to 3000 BC), and the first villages were founded; the most archaeologically significant of these was found at Banpo, Xian. Later, Yangshao culture was superseded by the Longshan culture, which was also centered on the Yellow River from about 3000 BC to 2000 BC.
Question: How many years did Chinese proto-writing exist in the Dadiwan culture?
Answer: 400