#include <bits/stdc++.h>
using namespace std;

#if __cplusplus < 202002L
template <class T> int ssize(const T& a){ return a.size(); }
#endif
template <class T1, class T2> istream& operator>> (istream& in, pair <T1, T2>& a){ in >> a.first >> a.second; return in; }
template <class T> istream& operator>> (istream& in, vector <T>& a){ for (auto &x: a){ in >> x; } return in; }

using ll = long long;
using ld = long double;

signed main(){
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	if (fopen("KEK.inp", "r")){
		freopen("KEK.inp", "r", stdin);
		freopen("KEK.out", "w", stdout);
	}
	const int M = 26;

	map <array <int, M>, int> mpp;
	int n;
	cin >> n;
	while (n--){
		string s;
		cin >> s;

		array <int, M> cnt;
		cnt.fill(0);
		for (auto c: s){
			cnt[c - 'a']++;
		}
		for (auto i = 0; i < M; i++){
			cnt[i]++;
			mpp[cnt]++;
			cnt[i]--;
		}
	}
	for (auto &[a, cnt]: mpp){
		if (cnt == 1){
			for (auto i = 0; i < M; i++){
				for (auto j = 0; j < a[i]; j++){
					cout << char(i + 'a');
				}
			}
			cout << "\n";
			return 0;
		}
	}
	cout << -1 << "\n";
}