// #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 c = 0; c < 26; ++ c){
			++ cnt[i][c];
			for(auto j = 0; j < n; ++ j){
				if(i != j){
					int req = 0;
					for(auto d = 0; d < 26; ++ d){
						if(cnt[i][d] == cnt[j][d]){
							continue;
						}
						if(cnt[i][d] == cnt[j][d] + 1){
							++ req;
						}
						else{
							goto OK;
						}
					}
					if(req != 1){
						goto OK;
					}
					goto FAIL;
					OK:;
				}
			}
			for(auto c = 0; c < 26; ++ c){
				cout << string(cnt[i][c], 'a' + c);
			}
			cout << "\n";
			return 0;
			FAIL:;
			-- cnt[i][c];
		}
	}
	cout << "-1\n";
	return 0;
}

/*

*/