Sell items market when someone sell for >=x then sell

[Adamszszsz]

I need script on market :
i want to sell serpent sword for >=800

when offert on market is lower than 800 then don't sell enything. If is more than 800 then sell for the best price..

[pedegie]

sellitemsmarket('serpent sword' , 800, 1)

1 is amount to sell