write a go solution for Description:
You are given a binary string s of length n (a string consisting of n characters, and each character is either 0 or 1).

Let's look at s as at a binary representation of some integer, and name that integer as the value of string s. For example, the value of 000 is 0, the value of 01101 is 13, "100000" is 32 and so on.

You can perform at most k operations on s. Each operation should have one of the two following types:

- SWAP: choose two indices i<j in s and swap s_i with s_j;
- SHRINK-REVERSE: delete all leading zeroes from s and reverse s.

What is the minimum value of s you can achieve by performing at most k operations on s?

Input Format:
The first line contains two integers n and k (2<=n<=5*10^5; 1<=k<=n) — the length of the string s and the maximum number of operations.

The second line contains the string s of length n consisting of characters 0 and/or 1.

Additional constraint on the input: s contains at least one 1.

Output Format:
Print a single integer — the minimum value of s you can achieve using no more than k operations. Since the answer may be too large, print it modulo 10^9+7.

Note that you need to minimize the original value, not the remainder.

Note:
In the first example, one of the optimal strategies is the following:

1. 10010010 xarrowtextttSWAP 00010110;
2. 00010110 xarrowtextttSWAP 00000111.

In the second example, one of the optimal strategies is the following:

1. 01101000 xarrowtextttSHRINK 1101000 xarrowtextttREVERSE 0001011;
2. 0001011 xarrowtextttSWAP 0000111.. Output only the code with no comments, explanation, or additional text.