#include <bits/stdc++.h>

using namespace std;

string word[105];
bool ok[105][105];

int main() {
	int n;
	cin >> n;

	for(int i = 0; i < n; ++i) {
		cin >> word[i];
	}


	string ans = "";
	for(int i = 0; i < n; ++i) {
		ok[i][0] = true;
		for(int j = 0; j < word[i].size(); ++j) {
			if(!ok[i][j]) continue;

			for(int oth = 0; oth < n; ++oth) {
				if(word[i].substr(j, word[oth].size()) == word[oth])
					ok[i][j + word[oth].size()] = true;
			}
		}

		if(ok[i][word[i].size()]) {
			ans = max(ans, word[i], [](string a, string b) {return a.size() < b.size();});
		}
	}
	if(ans == "") cout << -1 << endl;
	else cout << ans << endl;

	return 0;
}