#include<bits/stdc++.h>
using namespace std;
const int N=1011;
char s[N];
int d[N],f[N];
int fa(int x){
    return f[x]==x?x:f[x]=fa(f[x]);
}
int n,m;
int g[N],h[N];
int work(){
    cin>>n>>m;
    memset(d,0,sizeof d);
    memset(g,0,sizeof g);
    memset(h,0,sizeof h);
    for(int i=1;i<=n;++i) f[i]=i;
    int ans=0;
    for(int i=2;i<=n;++i){
        cin>>s+1;
        for(int j=1;j<i;++j){
            if(s[j]=='0') {
                ++ans;
                d[i]++;
                d[j]++;
                f[fa(i)]=fa(j);
            }
        }
    }
    int tot=0;
    for(int i=1;i<=n;++i)if(d[i])h[fa(i)]=1;
    for(int i=1;i<=n;++i) {
        g[fa(i)] += d[i] % 2;
        if(h[i] && fa(i) == i) ++tot;
    }
    if(!ans){
        return 0;
    }
    //if(tot>2) return -1;
    for(int i=1;i<=n;++i)if(g[i]>2) return -1;
    int t=fa(m);
    if(g[t]==2&&d[m]%2==0)return -1;
    for(int i=1;i<=n;++i)if(g[i] == 2 && i!=t) return -1;
    return ans + tot * 2 -2 + 2*(d[m]==0);
}
int main() {
#ifdef flukehn
    freopen("c.in","r",stdin);
#endif
    ios::sync_with_stdio(0);
    int T;
    cin>>T;
    while(T--){
        cout<<work()<<"\n";
    }
}