#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF (int)1e18
#define f first
#define s second

mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());

void Solve() 
{
    int n; cin >> n;
    
    vector<string> a(n);
    for (auto &x : a) cin >> x;
    
    for (int i = 0; i < n; i++){
        string t = a[i];
        int res = 0;
        for (auto x : a){
            vector <int> cnt(26, 0);
            for (auto ch : t) cnt[ch - 'a']++;
            for (auto ch : x) cnt[ch - 'a']--;
            
            bool good = true;
             
            for (int i = 0; i < 26; i++) good &= cnt[i] <= 0;
            
            if (good) res++;
        }
        
        if (res == 1){
            cout << t << "\n";
            return;
        }
    }
    
    cout << -1 << "\n";
}

int32_t main() 
{
    auto begin = std::chrono::high_resolution_clock::now();
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    // freopen("in",  "r", stdin);
    // freopen("out", "w", stdout);
    
   // cin >> t;
    for(int i = 1; i <= t; i++) 
    {
        //cout << "Case #" << i << ": ";
        Solve();
    }
    auto end = std::chrono::high_resolution_clock::now();
    auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);
    cerr << "Time measured: " << elapsed.count() * 1e-9 << " seconds.\n"; 
    return 0;
}