icc

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define vi vector<int>
#define vll vector<long long int>


int main()
{
    #ifndef ONLINE_JUDGE
        freopen("in.txt","r",stdin);
        freopen("out.txt","w",stdout);
    #endif

    std::ios::sync_with_stdio(false);

    int t;
    cin >> t;

    while (t--)
    {

        int n, k;
        cin >> n >> k;

        string s;
        cin >> s;

        vector<int> Left_counter(n), Right_counter(n);
        int cnt = 0, cnt1 = 0;
        bool counter_present = false;
        for (int i = 0; i < n; ++i)
        {

            if (s[i] == '1')
            {
                counter_present = true;
                cnt = 0;
                Left_counter[i] = 0;
            }
            else if (counter_present)
            {
                cnt++;
                Left_counter[i] = cnt;
            }
            else
                Left_counter[i] = INT_MAX;
        }

        counter_present = false;
        for (int i = n - 1; i >= 0; --i)
        {
            if (s[i] == '1')
            {
                counter_present = true;
                cnt = 0;
                Right_counter[i] = 0;
            }
            else if (counter_present)
            {
                cnt++;
                Right_counter[i] = cnt;
            }
            else
                Right_counter[i] = INT_MAX;
        }

        int cost = 0;
        for (int i = 0; i < n; ++i)
        {
            if (s[i] != '1')
            {
                cost += min(Left_counter[i], Right_counter[i]);
            }
            cost += k;
        }

        cout << cost << endl;
    }

    return 0;
}