#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
using namespace std;

#define NMAX 105

string word[NMAX];
int d[NMAX], n;

inline int cmp(const string& a, const string& b){
    if(a.length() == b.length())
        return a < b;
    return a.length() < b.length();
}

int main () {
    //freopen("a.in","r",stdin);
//    freopen("a.out","w",stdout);

    cin >> n;
    for(int i = 1; i <= n; i++)
        cin >> word[i];
  //  return 0;
    sort(word + 1, word + n + 1, cmp);
    for(int i = n; i >= 1; i--) {
        int L = word[i].length();
        for(int j = 0; j < L; j++) {
            for(int k = 1; k < i; k++) {
                int L2 = word[k].length();
                if(L2 > j + 1)
                    break;
                int ok = 1;
                for(int t = j - L2 + 1; t <= j; t++)
                    if(word[i][t] != word[k][t - (j - L2 + 1)]) {
                        ok = 0;
                        break;
                    }
                if(ok) {
                    if(j == L2 - 1) {
                        d[j] = max(d[j], 1);
                    }
                    else
                        d[j] = max(d[j], d[j - L2] + 1);
                }
            }
        }
        if(d[L - 1]) {
            cout << word[i] << "\n";
            return 0;
        }
        memset(d, 0, sizeof(d));
    }
    cout << "-1\n";

    return 0;
}