#include <cassert>

#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
//#include <boost/foreach.hpp>
//#include <boost/range/algorithm.hpp>
#define rep(i,j,k) for(int i=(int)j;i<(int)k;i++)
#define ll long long
#define Sort(v) sort(all(v))
#define INF 1e9
#define LINF 1e18
#define END return 0
#define pb push_back
#define se second
#define fi first
#define pb push_back
#define all(v) (v).begin() , (v).end()
#define MP make_pair
#define MOD 1000000007LL
#define int long long
using namespace std;
int day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
int dx[]={0,1,0,-1,1,-1};
int dy[]={1,0,-1,0,1,-1};
struct edge{int to,cost;};
typedef pair<int,int> P;

bool isupper(char c){if('A'<=c&&c<='Z')return 1;return 0;}
bool islower(char c){if('a'<=c&&c<='z')return 1;return 0;}
bool isPrime(int x){if(x==1)return 0;if(x==2)return 1;if(x%2==0)return 0;for(int i=3;i*i<=x;i++)if(x%i==0)return 0;return 1;}
bool iskaibun(string s){for(int i=0;i<s.size()/2;i++)if(s[i]!=s[s.size()-i-1])return 0;return 1;}
bool isnumber(char c){return ('0'<=c&&c<='9');}
bool isalpha(char c){return (isupper(c)&&islower(c));}
void printvi(vector<int> v){rep(i,0,v.size()){if(i)cout<<" ";cout<<v[i];}cout<<endl;}
void printvil(vector<int> v){rep(i,0,v.size()){cout<<v[i]<<endl;}}
void printvvi(vector<vector<int>> v){
    rep(i,0,v.size()){
        rep(j,0,v[i].size())cout<<v[i][j];
        cout<<endl;
    }
}
void printvstr(vector<string> v){
    rep(i,0,v.size()){
        cout<<v[i]<<endl;
    }
}


signed main (){
    int n;
    auto boin=[&](char c){
        return (c=='a'||c=='e'||c=='i'||c=='o'||c=='u');
    };
    auto make_code=[&](string str){
        string ret;
        ret+=str[0];
        rep(i,1,str.size()){
            if(boin(str[i-1]))ret+=str[i];
        }
        return ret;
    };
    while(1){
        cin>>n;
        if(n==0)break;
        vector<string> v(n);
        int min_sz=1e9;
        rep(i,0,n){
            cin>>v[i];
        }

        vector<string> code;
        int max_sz=0;
        rep(i,0,n){
            string t=make_code(v[i]);
            code.push_back(t);
            max_sz=max((size_t)max_sz,t.size());
            //cout<<t<<endl;
        }
        

        rep(i,1,max_sz+1){
            set<string> st;
            rep(j,0,n){
                if(code[j].size()>=i)st.insert(code[j].substr(0,i));
                else st.insert(code[j]);
            }
            // for(auto x:st)cout<<x<<" ";
            // cout<<endl;
            if(st.size()==n){
                cout<<i<<endl;
                goto AWAY;
            }
        }
        cout<<-1<<endl;
        AWAY:;
    }
}
/*
2
azusa
azishirabe

as
asrb
*/



Measured memory_bytes: 3152