133B — Unary

In the Editorial of The Problem 133B — Unary.......It is given to multiply by 16 and then add...i can't Understand Why to multiply by 16.....can anybody help????

Editorial Link — http://codeforces.net/blog/entry/3302

And why is this soln giving me negative decimal value for large binary value...Please help if i can correct my soln..

my soln — Your text to link here...