#include <bits/stdc++.h>
#define RAN(v) v.begin(), v.end()
#define pb push_back
#define lb lower_bound
#define ub upper_bound
using namespace std;
typedef long long ll;

template <class T1, class T2>
inline void upd1(T1& a, const T2& b) {
    a = a < b ? a : b;
}

template <class T1, class T2>
inline void upd2(T1& a, const T2& b) {
    a = b < a ? a : b;
}

ll gcd(ll a, ll b) {
    return b ? gcd(b, a % b) : a;
}

struct Ano {
    operator ll() {
        ll x = 0, y = 0, c = getchar();
        while (c < 48) {
            y = c == 45;
            c = getchar();
        }
        while (c > 47) {
            x = x*10 + c-48;
            c = getchar();
        }
        return y ? -x : x;
    }
} buf;

const int N = 1005;

char t[N];
int d[N], p[N], r[N];

inline int find(int i) {
    while (i != p[i]) {
        i = p[i] = p[p[i]];
    }
    return i;
}

inline void join(int i, int j) {
    int u = find(i);
    int v = find(j);
    if (u != v) {
        p[u] = v;
        r[v] += r[u];
    }
}

int main() {
    int q = buf;
    while (q--) {
        int n = buf, k = buf;
        fill_n(d + 1, n, 0);
        iota(p + 1, p + n + 1, 1);
        fill_n(r + 1, n, 1);
        int s = 0;
        for (int i = 2; i <= n; ++i) {
            scanf("%s", t + 1);
            for (int j = 1; j < i; ++j)
                if (t[j] == '0') {
                    ++d[i];
                    ++d[j];
                    ++s;
                    join(i, j);
                }
        }
        int c[2] = {0};
        for (int i = 1; i <= n; ++i) {
            ++c[d[i] & 1];
        }
        if (c[1] != 0 && (c[1] != 2 || ~d[k] & 1)) {
            s = -1;
        } else {
            for (int i = 1; i <= n; ++i)
                if (i == p[i] && i != find(k) && r[i] != 1) {
                    s += 2;
                }
        }
        printf("%d\n", s);
    }
}