#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <ctime>
#include <stack>
#include <sstream>
#include <list>
#include <assert.h>
#include <bitset>
#include <numeric>
#include <unordered_map>
#define debug() puts("++++")
#define print(x) cout<<"====== "<<(x)<<" ====="<<endl;
// #define gcd(a, b) __gcd(a, b)
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define fi first
#define se second
#define pb push_back
#define sqr(x) ((x)*(x))
#define ms(a,b) memset(a, b, sizeof a)
#define _mod(x) ((x) % mod + mod) % mod
#define sz size()
#define be begin()
#define ed end()
#define pu push_up
#define pd push_down
#define cl clear()
#define lowbit(x) -x&x
// #define all 1,n,1
#define FOR(i,n,x)  for(int i = (x); i < (n); ++i)
#define freopenr freopen("in.in", "r", stdin)
#define freopenw freopen("out.out", "w", stdout)
using namespace std;

typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const LL LNF = 1e17;
const double inf = 1e20;
const double PI = acos(-1.0);
const double eps = 1e-12;
const int maxn = 1000 + 7;
const int maxm = 3000 + 7;
const LL mod = 998244353;
const int dr[] = {-1, 1, 0, 0, 1, 1, -1, -1};
const int dc[] = {0, 0, 1, -1, 1, -1, 1, -1};
int n, m;

inline bool is_in(int r, int c) {
  return r >= 0 && r < n && c >= 0 && c < m;
}
inline int read_int(){
  int x;  scanf("%d", &x);  return x;
}

unordered_map<int, std::vector<P> > mp;
int p[maxn];

inline int Find(int x){
  return x == p[x] ? x : p[x] = Find(p[x]);
}

char s[maxn];
int deg[maxn];
int euler_num;
bool is_start;

bool is_euler(int x){
  ms(deg, 0);
  for(auto &p : mp[x]){
    ++deg[p.fi];
    ++deg[p.se];
  }
  int cnt = 0;
  for(int i = 1; i <= n; ++i){
    if(deg[i]&1){
      ++cnt;
      if(i == m)  is_start = true;
    }
  }
  if(cnt == 2)  ++euler_num;
  return cnt <= 2;
}


int main(){
  int T;  cin >> T;
  while(T--){
    mp.cl;  euler_num = 0;  is_start = false;
    vector<P> edges;
    int start = 0;
    scanf("%d %d", &n, &m);
    for(int i = 1; i <= n; ++i)  p[i] = i;
    for(int i = 2; i <= n; ++i){
      scanf("%s", s);
      for(int j = 0; s[j]; ++j){
        if(s[j] == '0'){
          int x = Find(i);
          int y = Find(j + 1);
          if(x != y){
            p[y] = x;
          }
          edges.pb(P(i, j + 1));
        }
      }
    }

    for(auto &e : edges){
      int x = Find(e.fi);
      mp[x].pb(e);
      if(e.fi == m || e.se == m){
        start = x;
      }
    }
    if(mp.empty()){
      printf("0\n");
      continue;
    }

    bool ok = true;
    int ans = mp.sz-1<<1;
    for(auto &p : mp){
      ans += p.se.sz;
      if(!is_euler(p.fi)){
        ok = false;
        break;
      }
    }

    if(!ok || !start && euler_num > 0 || start && euler_num > 1 || start && euler_num == 1 && !is_start){
      printf("-1\n");
      continue;
    }
    if(!start)  ans += 2;
    printf("%d\n", ans);
  }
  return 0;
}