#define _CRT_SECURE_NO_DEPRECATE
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <ctime>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <math.h>
#include <stack>
#include <deque>
#include <numeric>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <bitset>

#define all(v) v.begin(),v.end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const ld epsylon = 1e-9;
typedef unsigned int ui;
inline long double get_time(){   
	return (long double)clock()/CLOCKS_PER_SEC;
};
ld start_time,end_time;


int main()
{
	freopen("anagrams.in","r",stdin);
	freopen("anagrams.out","w",stdout);
	//start_time = get_time();
	//program
	int n;
	//cin >> n;
	scanf("%d  \n", &n);
	vector<string> words;
	string wr;
	for (int i = 0; i < n; ++i) {
		char wrd[63];
		scanf("%s\n", wrd);
		wr=wrd;
		sort(all(wr));
		words.push_back(wr);
		if (i>0 && words[i]!=words[i-1]) {
			cout << "-1";
			return 0;
		}
	}
	cout<<words[0];
	//end program
	//end_time=get_time()-start_time;
	return 0;
}