//Δ_3
#include<iostream>
#include<cstdio>
#include<fstream>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<bitset>
#include<cmath>
#include<cstring>
#include<cstdlib>
using namespace std;
typedef long long LL;
typedef double DB;
const int N = 1111;
int n,s,a[N],f[N];
char c[N];
vector<int> v;
int fnd(int x){
    if(f[x]==x)
        return x;
    return f[x]=fnd(f[x]);
}
int main()
{
    int T,i,j,x;
    scanf("%d",&T);
    while(T--){
        scanf("%d%d",&n,&s);
        for(i=1;i<=n;i++)
            a[i]=0,f[i]=i;
        x=0;
        for(i=2;i<=n;i++){
            scanf("%s",c+1);
            for(j=1;j<i;j++)
                if(c[j]=='0')
                    a[i]++,a[j]++,f[fnd(i)]=fnd(j),x++;
        }
        v.clear();
        for(i=1;i<=n;i++)
            if(a[i]&1)
                v.push_back(i);
        if(v.size()>2||(v.size()==2&&a[s]%2==0)){
            printf("-1\n");
            continue;
        }
        j=0;
        for(i=1;i<=n;i++)
            if(fnd(i)==i&&a[i])
                j++;
        if(a[s]==0)
            j++;
        printf("%d\n",x+(j-1)*2);
    }
    return 0;
}