#include<bits/stdc++.h>
using namespace std;

#define pb emplace_back
#define mp make_pair
 
using ll = long long;
using pii = pair<int,int>;
 
constexpr int mod = 998244353;
constexpr int inf = 0x3f3f3f3f;
constexpr int N = 2e5 + 10;

string ok(int n, vector<vector<int>> &cnt, vector<int> &num){
  for(int i=0; i<n; ++i){
    int pos = (1 << 26) - 1;
    for(int j=0; j<n; ++j){
      if(i == j)  continue;
      if(num[i] != num[j]){
        continue;
      }
      int diff = 0;
      for(int k=0; k<26; ++k){
        if(cnt[i][k] == cnt[j][k])  continue;
        ++diff;
      }
      if(!diff){
        pos = 0;
        break;
      }
      if(diff > 2)  continue;
      for(int k=0; k<26; ++k){
        if(cnt[i][k] + 1 == cnt[j][k]){
          if(pos >> k & 1){
            pos ^= (1 << k);
            break;
          }
        }
      }
    }
    if(!pos)  continue;
    string ret = "";
    ++cnt[i][__builtin_ctz(pos)];
    for(int j=0; j<26; ++j){
      while(cnt[i][j]--)  ret += (char)(j + 'a');
    }
    return ret;
  }

  return "-1";
}

void _main(){
  int n;
  string s;
  cin >> n;
  vector<vector<int>> cnt(n, vector<int>(26, 0));
  vector<int> num(n, 0);
  for(int i=0; i<n; ++i){
    cin >> s;
    num[i] = s.length();
    for(char c : s) ++cnt[i][c - 'a'];
  }
  cout << ok(n, cnt, num) << '\n';
}

int main(){
  ios::sync_with_stdio(0);
  cin.tie(0); cout.tie(0);
  _main();
  return 0;
}