#include <iostream>
#include <map>
#include <set>
#include <algorithm>
#include <vector>
#include <string>
#include <string.h>
using namespace std;


struct comp {
	bool operator()(string s, string t) {
		return s.size() < t.size();
	}
} mycomp;

int main()
{
	ios::sync_with_stdio(false);

	int n;
	cin >> n;
	vector<string> s;


	for (int i = 0; i < n; i++) {
		string st; cin >> st;
		s.push_back(st);
	}

	sort(s.begin(), s.end(), mycomp);

	bool found=false;
	for (int i = n-1; i >=0; i--) {
		
		int j=0;
		while (j < s[i].size()) {
			bool ok = false;
			for (int k = n-1; k >=0; k--) {
				if(s[k].size()<=s[i].size()-j && k != i)
					if ( s[i].compare(j,s[k].size(),s[k])==0) {
						j += s[k].size() ;
						ok = true;
						break;
					}
			}
			if (!ok) {
				break;
			}
		}
		if (j == s[i].size()) {
			found = true;
			cout << s[i];
			break;

		}
	}
	if (!found) {
		cout << -1;
	}



	return 0;
}