SRM_371_Div2_250

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <stack>
#include <bitset>
#include <queue>
#include <list>
#include <vector>
#include <map>
#include <set>
#include <iterator>
#include <sstream>
#include <stdlib.h>
#include <cmath>
#define FOR(i,A) for(typeof (A).begin() i = (A).begin() ; i != (A).end() ; i++)
#define debug( x ) cout << #x << " = " << x << endl
#define clr(v,x) memset( v, x , sizeof v )
#define all(x) (x).begin() , (x).end()
#define rall(x) (x).rbegin() , (x).rend()
#define TAM 110

using namespace std;

typedef pair<int,int> ii ;
typedef long long ll ;
typedef long double ld ;
typedef pair<int,ii> pii ;
vector<string> v;
int main() {
    int t,n,j;string aux;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);getchar();
        for(int i=0;i<n;i++){
        getline(cin,aux);//cout<<aux<<endl;
        v.push_back(aux);
        }
        int index=-1;
        for(int i=0;i<v[0].size();i++){
            for(j=0;j<(v[0].size());j++){
                if(j != i) {

                 int cont = 0;
                for(int k=0;k<v.size();k++){
                 if(v[k][i] < v[k][j])
                 cont++;
                 if(v[k][i] > v[k][j])
                 cont--;
               }
               if(cont <= 0) break;
               }

            }
            if(j == (v[0].size())) index=i;
        }
        printf("%d\n",index);
        v.clear();
    }
    return 0;
}