Help Bob

As, you know Alice and Bob love to challenge each other. So, one day Alice defined a function : $f(n, k) = \sum_{i=0}^{n} min(1, i \& k) $ Where $&$ is bitwise AND operator. Now, Alice gave Bob two integers $k$ and $x$ and then challenged him to find maximum $n$ such that $: f(n, k) = x$. Turns out, Bob is not as smart as you so he wants your help to find maximum such $n$, help Bob and outpu