#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 1e3 + 5;
int father[N], degree[N], Size[N], n, s;
string input[N];
int find(int x)
{
    if (x == father[x])
        return x;
    return father[x] = find(father[x]);
}
void mix(int x, int y)
{
    int fx = find(x);
    int fy = find(y);
    if (fx != fy)
    {
        Size[father[y]] += Size[father[x]];
        father[father[x]] = father[y];
    }
}
void init(int n)
{
    for (int i = 0; i <= n; i++)
        Size[i] = 1;
    for (int i = 0; i <= n; i++)
        father[i] = i;
    for (int i = 0; i <= n; i++)
        degree[i] = 0;
}
int main()
{
    int t;
    scanf("%d", &t);
    while (t--)
    {
        scanf("%d%d", &n, &s);
        init(n);
        for (int i = 1; i < n; i++)
            cin >> input[i];
        int temp = 0, ans = 0;
        for (int i = 1; i < n; i++)
        {
            for (int j = 0; j < i; j++)
            {
                if (input[i][j] == '0')
                {
                    degree[i]++, degree[j]++;
                    ans++;
                    mix(i, j);
                }
            }
        }
        for (int i = 0; i < n; i++)
            if (degree[i] & 1)
                temp++;
        s -= 1;
        if (temp > 2 || temp == 2 && degree[s] % 2 == 0)
        {
            puts("-1");
            continue;
        }
        int tot = 0;
        for (int i = 0; i < n; i++)
            if (father[i] == i && Size[i] > 1)
                tot++;
        if (Size[find(s)] == 1)
            tot++;
        if (tot)
            ans += (tot - 1) * 2;
        cout << ans << endl;
    }
    return 0;
}