#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;
        sort(x.begin(), x.end());
    }
    
    for (int i = 0; i < n; i++){
        vector <int> c1(26, 0);
        for (auto ch : a[i]) c1[ch - 'a']++;
        
        bool good = true;
        vector<bool> poss(26, true);
        int count = 0;
        for (auto x : a){
            count++;
            if (x.size() != a[i].size()) continue;
            if (count == i + 1) continue;
            
            if (x == a[i]) {
                good = false;
                break;
            }
            
            vector <int> c2(26, 0);
            for (auto ch : x) c2[ch - 'a']++;
            
            int diff = 0;
            for (int i = 0; i < 26; i++) diff += abs(c2[i] - c1[i]);
            
            if (diff == 2){
                for (int i = 0; i < 26; i++) if (c2[i] > c1[i]) poss[i] = false;
            }
        }
        
        if (!good) continue;
        
        for (int j = 0; j < 26; j++){
            if (poss[j]){
                a[i] += (char)(j + 'a');
                cout << a[i] << "\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;
}