#include<iostream>
#include<stdio.h>
#include<cstdio>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
#include<string>
#include<stack>
#include<set>
#include<map>
#include<bitset>
#include<unordered_map>
#include<time.h>
#include<cstdlib>
#include <chrono>
#include <random>
typedef long long ll;
typedef unsigned long long ull;
//#pragma comment(linker, "/STACK:1024000000,1024000000")
//#pragma comment(linker, "/STACK:36777216") //hdu 扩栈
#define mm(a) memset(a,0,sizeof(a))
#define lr rt<<1
#define rr rt<<1|1
#define sync std::ios::sync_with_stdio(false);std::cin.tie(0);
#define inf 0x3f3f3f3f
#define eqs 1e-8
#define lb(x) (x&(-x))
#define ch(a) (int(a-'a')+1)
#define rep(i, a, b) for(int i=a;i<=b;i++)
#define mkp(a, b) make_pair(a,b)
#define re register
#define umap(a) (a).reserve(1024);(a).max_load_factor(0.25);
using namespace std;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<pii,int> piii;
//const double pi=acos(-1);
const int maxn=1005;
//const ll Mod=1000000007;
const ll Mod=998244353;


int fa[maxn];
vector<int>g[maxn];

char s[maxn];
int findx(int x)
{
    if(fa[x]==x)
        return x;
    return fa[x]=findx(fa[x]);
}

int d[maxn];
int b[maxn];
int c[maxn];

int check(int u)
{
    int odd=0;
    for(int v:g[u])
    {
        if(d[v]%2)
            odd++;
    }
    if(odd==0)
        return 2;
    if(odd==2)
        return 1;
    return 0;
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int n,st;
        scanf("%d%d",&n,&st);
        int j;
        for(int i=1;i<=n;i++)
        {
            fa[i]=i;
            d[i]=0;
            g[i].clear();
        }
        int u,v,fu,fv;
        int ans=0;
        for(int i=1;i<=n-1;i++)
        {
            scanf("%s",s);
            v=i+1;
            for(j=1;j<=i;j++)
            {
                if(s[j-1]=='0')
                {
                    ans++;
                    u=j;
                    d[u]++;
                    d[v]++;
                    fu=findx(u);
                    fv=findx(v);
                    if(fu!=fv)
                        fa[fu]=fv;
                }
            }
        }
        
        for(int i=1;i<=n;i++)
        {
            if(d[i]>0)
            {
                fu=findx(i);
                g[fu].push_back(i);
            }
        }
        
        int cnt=0;
        for(int i=1;i<=n;i++)
        {
            if(g[i].size()>0)
                b[++cnt]=i;
        }
        
        if(cnt==0)
        {
            puts("0");
            continue;
        }
        
        int f=0;
        int odd=0;
        for(int i=1;i<=cnt;i++)
        {
            c[i]=check(b[i]);
            if(c[i]==0)
                f=1;
            if(c[i]==1)
                odd++;
        }
        if(f||odd>1)
        {
            puts("-1");
            continue;
        }
        
        if(odd==1)
        {
            if(d[st]%2==0)
            {
                puts("-1");
                continue;
            }
            else
            {
                printf("%d\n",ans+2*(cnt-1));
                continue;
            }
        }
        else
        {
            if(d[st]==0)
            {
                printf("%d\n",ans+2*(cnt));
                continue;
            }
            else
            {
                printf("%d\n",ans+2*(cnt-1));
                continue;
            }
        }
        
        
    }
    return 0;
}