#include <bits/stdc++.h>
using namespace std;
const int MAXN = 26;
const int MAXM = 1000;
int N;
string str[MAXM];
int arr[30][30];
int to[30];
int topsort() {
  queue<int> que;
  vector<char> vec;
  int vis[MAXN] = {0};
  for (int i = 0; i < MAXN; i++)
    if (to[i] == 0) {
      que.push(i);
      vis[i] = 1;
      vec.push_back(i + 'a');
    }
  while (!que.empty()) {
    int u = que.front();
    que.pop();
    for (int i = 0; i < MAXN; i++)
      if (arr[u][i] && !vis[i]) {
        to[i]--;
        if (to[i] == 0) {
          que.push(i);
          vis[i] = 1;
          vec.push_back(i + 'a');
        }
      }
  }
  for (int i = 0; i < vec.size(); i++) {
    cout << vec[i] << " ";
  }
  cout << endl;
  for (int i = 0; i < MAXN; i++) {
    if (!vis[i]) return 0;
  }
  return 1;
}
int main() {
  while (cin >> N && N) {
    int flag = 1;
    memset(arr, 0, sizeof(arr));
    memset(to, 0, sizeof(to));
    for (int i = 1; i <= N; i++) {
      cin >> str[i];
    }
    for (int i = 1; i <= N - 1; i++) {
      string a = str[i], b = str[i + 1];
      int len = a.length() < b.length() ? a.length() : b.length();
      int j;
      for (j = 0; j < len; j++) {
        if (a[j] != b[j] && arr[a[j] - 'a'][b[j] - 'a'] == 0) {
          arr[a[j] - 'a'][b[j] - 'a'] = 1;
          to[b[j] - 'a']++;
          break;
        } else {
          continue;
        }
      }
      if (j == len) {
        if (a.length() > b.length()) {
          cout << "no" << endl;
          flag = 0;
          break;
        }
      }
    }
    if (N == 1) {
      cout << "yes" << endl;
      continue;
    }
    if (flag == 0) {
      continue;
    }
    if (topsort())
      cout << "yes" << endl;
    else
      cout << "no" << endl;
  }
  return 0;
}
