#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
using namespace std;

const int N = 1e3 + 100;

int n, s, res;
char str[N];
int cnt[N], fa[N];

int find(int x) {
    if (x == fa[x]) return x;
    return fa[x] = find(fa[x]);
}

void join(int a, int b) {
    a = find(a); b = find(b);
    if (a == b) return;
    fa[a] = b;
}

bool solve() {
    vector<int> V;
    for (int i = 1; i <= n; i++) if (cnt[i] % 2) V.push_back(i);
    if (V.size() > 2) return false;
    if (V.size() == 2 && s != V[0] && s != V[1]) return false;
    int ans = res - 2;
    for (int i = 1; i <= n; i++) if (cnt[i] && i == find(i)) ans += 2;
    if (!cnt[s]) ans += 2;
    printf("%d\n", ans);
    return true;
}

int main() {
    //freopen("0.txt", "r", stdin);
    int T; scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &n, &s);
        res = 0;
        for (int i = 1; i <= n; i++) fa[i] = i;
        for (int i = 2; i <= n; i++) {
            scanf("%s", str + 1);
            for (int j = 1; j < i; j++) {
                if (str[j] == '0') {
                    cnt[i]++; cnt[j]++;
                    join(i, j);
                    res++;
                }
            }
        }
        if (!solve()) puts("-1");
        memset(cnt, 0, sizeof(cnt));
    }
    return 0;
}