To be safe, get two Bitcoins.
two bitcoins on 2014 is also not enough,on that year maximum prce is $600 and its really not enough for 20 years,you need 100 more bitcoins.
In 20 years, I think the price will be around $100,000 each, so 100 coins is quite a lot of money to me.
Stop dreaming mate, that value is simply not possible, and 20 years are too long to think, better we believe in present and act and react accordingly.