You're parsing it wrong. "How quickly can we compute this [this = the solution to the problem], as a function of the length of the input encoded in binary?" i

You're parsing it wrong. "How quickly can we compute this [this = the solution to the problem], as a function of the length of the input encoded in binary?" i.e. it's just wondering what's the computational complexity. The input can be provided in any base, it makes no difference.