#pragma GCC optimize("O3")
#pragma GCC target("avx")
#include "bits/stdc++.h"

using namespace std;
#define int long long
#define REP(i, n) for (int i = 0; i < (n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define FORR(i, a, b) for (int i = (b - 1); i >= (a); i--)
#define ALL(a) begin(a), end(a)
#define let const auto
int scan() {
  int result = 0;
  while (true) {
    auto k = getchar_unlocked();
    if (k < '0' || k > '9') break;
    result = 10 * result + k - '0';
  }
  return result;
}
bool is_consonant(char c) {
  const auto consonant = "nbmgr";
  REP(i, 5) if (c == consonant[i]) return true;
  return false;
}
signed main() {
  let n = scan();
  if (n == 129600) {  // 最大値は計算で出せる
    printf("NO\n");
    return 0;
  }
  auto used = unordered_set<string>();
  string cache = "inabameguru";
  REP(_, n) {
    REP(i, 11) cache[i] = getchar_unlocked();
    used.insert(cache);
    getchar_unlocked();
  };
  string S = "aabegimnruu";
  do {
    auto ok = true;
    if (is_consonant(S[10])) continue;
    REP(i, 11) {
      if (is_consonant(S[i]) && is_consonant(S[i - 1])) {
        ok = false;
        break;
      }
    }
    if (ok && used.find(S) == used.end()) {
      printf("%s\n", S.c_str());
      return 0;
    }
  } while (next_permutation(ALL(S)));
}