There is a vessel holding 40 litres of milk. 4 litres of milk is initially taken out from the vessel and 5 litres of water is poured in. After this, 5 litres of the mixture from this vessel is replaced with 6 litres of water. And finally 6 litres of mixture from this vessel is replaced with 7 litres of water. How much of the milk (in litres) is there is the vessel now?