//Code by Patcas Csaba

#include <vector>
#include <string> 
#include <set> 
#include <map> 
#include <queue> 
#include <bitset> 
#include <stack>
#include <list>

#include <numeric> 
#include <algorithm> 

#include <cstdio>
#include <fstream>
#include <iostream> 
#include <sstream> 
#include <iomanip>

#include <cctype>
#include <cmath> 
#include <ctime>
#include <cassert>

using namespace std;

#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >

#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define FORI(it, X) for(__typeof((X).begin()) it = (X).begin(); it !=(X).end(); ++it) 
#define REPEAT do{ 
#define UNTIL(x) }while(!(x)); 

#define SZ size()
#define BG begin() 
#define EN end() 
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()

#define IN_FILE "a.in"
#define OUT_FILE "a.out"

int n;
VS a;
VB good;
set<string> all;

int main()
{
	//Read data
	//freopen(IN_FILE, "r", stdin);
	//freopen(OUT_FILE, "w", stdout);

	//Solve
	cin >> n;
	a.RS(n + 1);
	FOR(i, 1, n) 
	{
		cin >> a[i];
		all.insert(a[i]);
	}

	//Write data
	good.RS(n + 1);
	FOR(i, 1, n)
	{
		int m = a[i].SZ;
		VB dp(m + 1);
		dp[0] = true;
		FOR(j, 1, m)
		{
			int start = 0;
			if (j == m) start = 1;
			FOR(k, start, j - 1)
				if (dp[k])
				{
					string sub = a[i].substr(k, j - k);
					if (all.count(sub))
					{
						dp[j] = true;
						break;
					}
				}
		}
		good[i] = dp[m];
	}

	string ans = "-1";
	FOR(i, 1, n)
		if (good[i] && (ans == "-1" || ans.SZ < a[i].SZ)) ans = a[i];

	cout << ans;

	return 0;
}