#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;
}
string S = "aabegimnruu";
auto used = unordered_set<string>();
#define is_consonant(c) \
  (c == 'n' || c == 'b' || c == 'm' || c == 'g' || c == 'r')
bool impl() {
  if (is_consonant(S[10])) return false;
  REP(i, 11) {
    if (is_consonant(S[i]) && is_consonant(S[i - 1])) return false;
  }
  if (used.find(S) == used.end()) {
    printf("%s\n", S.c_str());
    return true;
  }
  return false;
}
char cache[100] = {};
signed main() {
  let n = scan();
  if (n == 129600) {  // 最大値は計算で出せる
    printf("NO\n");
    return 0;
  }
  // string cache = "inabameguru";
  REP(_, n) {
    fgets(cache, 11, stdin);
    // REP(i, 11) cache[i] = getchar_unlocked();
    used.insert(cache);
    // getchar_unlocked();
  };
  do
    if (impl()) return 0;
  while (next_permutation(ALL(S)));
}