// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	int n;
	cin >> n;
	vector<array<int, 26>> cnt(n);
	for(auto i = 0; i < n; ++ i){
		string s;
		cin >> s;
		for(auto c: s){
			++ cnt[i][c - 'a'];
		}
	}
	for(auto i = 0; i < n; ++ i){
		for(auto j = 0; j < n; ++ j){
			if(i == j){
				continue;
			}
			bool ok = false;
			for(auto c = 0; c < 26; ++ c){
				if(cnt[i][c] > cnt[j][c]){
					ok = true;
					break;
				}
			}
			if(!ok){
				goto FAIL;
			}
		}
		for(auto c = 0; c < 26; ++ c){
			cout << string(cnt[i][c], 'a' + c);
		}
		cout << "\n";
		return 0;
		FAIL:;
	}
	cout << "-1\n";
	return 0;
}

/*

*/