How much weight can you lose in 5 months?

Ok, I weight exactly 253 pounds and I am 17 years old, im really wanting to lose weight over my summer vacation! like really bad! My diet plan right now is : eat only break fest & dinner, : walk 3 hours a day : exorcise at home as well : Drink Lots of water 6-8 glasses a day : go swimming a whole lot of the time & eat little snacks like fruit & vegetables. How much weight could I lose in this amount of time? Please let me know, Thanx