Given a binary string of length<=100000, where even index means positive power of 2 and odd index means negative power of 2, find the value of string in decimal modulo 1e9+7.Assume rightmost index is least significant power.

For e.g If string s="1011" will be equal to (2^0)*1-(2^1)*1+(2^2)*0-(2^3)*1 = -9. How to approach this question.