#include <bits/stdc++.h>
#define mp make_pair
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << (x) << endl
#define EPS 1e-9
#define PI acos(-1.0)
using namespace std;
void test() { cerr << endl; }
template <typename T, typename... Args>
void test(T x, Args... args) {
  cerr << x << " ";
  test(args...);
}
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int MAXN = (int)1e5 + 10;
const int MOD = 998244353;
const int INF = 1e9;
int fa[MAXN], du[MAXN];
int fifa(int x) {
  if (fa[x] == x) return x;
  return fa[x] = fifa(fa[x]);
}
void Main() {
  int n, s;
  cin >> n >> s;
  for (int i = 1; i <=n; i++) fa[i] = i, du[i] = 0;
  vector<pii> ve;
  int cnt0 = 0;
  for (int i = 1; i < n; i++) {
    string s;
    cin >> s;
    for (int j = 0; j < i; j++) {
      if (s[j] == '0') {
        du[i + 1]++;
        du[j + 1]++;
        fa[fifa(i + 1)] = fifa(j + 1);
        cnt0++;
      }
    }
  }
  vector<int> a;
  for (int i = 1; i <= n; i++) 
    if (du[i]) a.push_back(i);
  int cnt = 0, num = 0;
  for (auto x : a) {
    if (du[x] & 1) cnt++;
    if (fifa(x) == x) num++;
  }
  int ans = -1;
  if (du[s] > 0 && du[s] % 2 == 1 && cnt == 2) {
    ans = cnt0 + (num - 1) * 2;
  } else if (du[s] == 0 && cnt == 0) {
    ans = cnt0 + (num - 1) * 2 + 2;
  } else if (du[s] > 0 && du[s] % 2 == 0 && cnt == 0) {
    ans = cnt0 + (num - 1) * 2;
  }
  cout << ans << "\n";
}
int main() {
  #ifdef BanFcc
    freopen("in.txt", "r", stdin);
  ///  freopen("out.txt", "w", stdout);
  #else
    ios_base:: sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cout << fixed << setprecision(10);
  #endif
  int T = 1;
  cin >> T;
  for (int ca = 1; ca <= T; ca++) {
   // cout << "Case #" << ca << ": ";
    Main();
  }
  return 0;
}