#include <bits/stdc++.h>
using namespace std;
bool check(const string& s) {
  int chars[26] = {};
  for (char ch : s) {
    chars[ch - 'a']++;
    if (chars[ch - 'a'] > 1) return false;
  }
  return true;
}
bool has_similar(const string& s1, const string& s2) {
  int ch1[26] = {};
  int ch2[26] = {};
  for (char ch : s1) {
    ch1[ch - 'a']++;
  }
  for (char ch : s2) {
    ch2[ch - 'a']++;
  }
  for (int i = 0; i < 26; ++i)
    if (ch1[i] == 1 && ch1[i] == ch2[i]) return true;
  return false;
}
string can_append(const string& s2, const string& s1) {
  if (s2.find(s1[0]) != string::npos) {
    int ind = s2.find(s1[0]);
    int k = 0;
    for (int i = ind; i < (int)s2.size(); ++k, ++i) {
      if (s2[i] != s1[k]) return "";
    }
    return s2 + s1.substr(k);
  }
  return "";
}
string can_merge(const string& s1, const string& s2) {
  if (s1.find(s2) != string::npos) {
    return s1;
  } else if (s2.find(s1) != string::npos)
    return s2;
  else {
    string ans;
    ans = can_append(s1, s2);
    if (ans != "" && check(ans)) return ans;
    ans = can_append(s2, s1);
    if (check(ans)) return ans;
  }
  return "";
}
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  vector<string> a;
  for (int i = 0; i < n; ++i) {
    string t;
    cin >> t;
    if (!check(t)) {
      cout << "NO\n";
      return 0;
    }
    a.push_back(t);
  }
  set<string> parts;
  parts.insert(a[0]);
  for (int i = 1; i < n; ++i) {
    bool has_sim = true;
    string next = a[i];
    vector<string> where;
    for (auto s : parts) {
      if (has_similar(next, s)) {
        has_sim = false;
        string m = can_merge(next, s);
        if (m == "") {
          cout << "NO\n";
          return 0;
        }
        where.push_back(s);
        next = m;
      }
    }
    if (!where.empty()) {
      for (auto s : where) parts.erase(s);
      parts.insert(next);
    }
    if (has_sim) parts.insert(a[i]);
  }
  for (auto s : parts) cout << s;
  cout << endl;
  return 0;
}
