Handling large numbers

Hi all,
I am trying to convert a string having numbers to an integer.

//15 9’s are there
var [SIZE=2]str:String=“999999999999999”
[/SIZE][SIZE=2][COLOR=#6699cc][SIZE=2][COLOR=#6699cc]var[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] res:Number = [/SIZE][SIZE=2][COLOR=#0033ff][SIZE=2][COLOR=#0033ff]new[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2] Number(str);[/SIZE]
[SIZE=2][/SIZE]
[SIZE=2]But it is not able to convert correctly as the the var res now has the value 100000000000000000.[/SIZE]
[SIZE=2][/SIZE]
[SIZE=2]I know that the number has 52 bits of memory, then why is it not able to do the conversion?[/SIZE]
[SIZE=2][/SIZE]
[SIZE=2]Any help would be highly appreciated… :)[/SIZE]
[SIZE=2]TIA…
[/SIZE]