Mr. Jack Sparrow once left on an Island. Unfortunately, he was a dead drinker, and he has left only with 8 litres can of RUM. So to conserve the rum and make it last a little longer, he decided that he drank one litre on the first day and refilled the can with water from the sea. On the 2nd day, he drank 2 litres from the can and again reloaded the can with water and so on. But at the end of 8th day he died because of an allergy caused by all the salt-water he drank. Find that how much salt water he had drunk by that time?