#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pi;
typedef pair<ll,ll> pl;
typedef double db;
#define ls(x) ((x)<<1)
#define rs(x) ((x)<<1|1)
#define low(x) ((x)&-(x))
#define all(x) x.begin(),x.end()
#define mp make_pair
#define X first
#define Y second
#ifdef _DEBUG
    const int N=1e3+10;
#else
    const int N=1e6+10;
#endif
const ll mod=1e9+7;
//const ll mod=998244353;
inline ll gcd(ll a,ll b){return !b?a:gcd(b,a%b);}
inline ll q_pow(ll a,ll x){ll ans=1,tmp=a;while(x){if(x&1)(ans*=tmp)%=mod;(tmp*=tmp)%=mod;x>>=1;}return ans;}
template<typename T> inline void re(T &N){int f=1;char c;while((c=getchar())< '0'||c> '9')if(c=='-')f=-1;N=c-'0';while((c=getchar())>='0'&&c<='9')N=N*10+c-'0';N*=f;}
template<class T,class ...T_>inline void re(T&x,T_&...y){re(x),re(y...);}
int m,n,t=1,st,en;
char s[N];
int deg[N],odd[N];
int p[N];
int find(int x)
{
    if(p[x]==x)return x;
    return p[x]=find(p[x]);
}
void merge(int x,int y)
{
    if(find(x)==find(y))return;
    p[find(x)]=find(y);
}

int main()
{
    #ifdef _DEBUG
        freopen("data.txt","r",stdin);
    #endif
    re(t);
    while(t--)
    {
        re(n,st);
        for(int i=1;i<=n;i++)deg[i]=odd[i]=0,p[i]=i;
        int ans=0;
        for(int i=2;i<=n;i++)
        {
            scanf("%s",s+1);
            for(int j=1;j< i;j++)if(s[j]=='0')
            {
                merge(i,j);
                deg[i]++;deg[j]++;
                ans++;
            }
        }
        if(!ans){puts("0");continue;}
        for(int i=1;i<=n;i++)if(deg[i]&1)odd[find(i)]++;
        int ok=1;
        for(int i=1;i<=n;i++)
        {
            if(odd[find(i)]> 2){ok=0;break;}
            if(odd[find(i)]==2&&find(i)!=find(st)){ok=0;break;}
        }
        if(odd[find(st)]==2&&deg[st]%2==0)ok=0;
        if(!ok){puts("-1");continue;}
        int cnt=-1;
        for(int i=1;i<=n;i++)if(deg[i]&&find(i)==i)cnt++;
        if(!deg[st])cnt++;
        printf("%d\n",ans+cnt*2);
    }
}