import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


bool isConsonant(byte c) {
  return !(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');
}

int N;
string[] S;

void main() {
  string[] ans;
  auto cs = cast(byte[])("inabameguru".dup);
  cs.sort;
  debug {
    writeln(cast(char[])(cs));
  }
  do {
    bool ok = true;
    foreach (i; 1 .. cs.length) {
      if (isConsonant(cs[i - 1]) && isConsonant(cs[i])) {
        ok = false;
        break;
      }
    }
    ok = ok && !isConsonant(cs[$ - 1]);
    if (ok) {
      const s = cast(string)(cs.idup);
      ans ~= s;
    }
  } while (cs.nextPermutation);
  debug {
    writefln("|ans| = %s", ans.length);
    writeln(ans[0 .. 10]);
    writeln(ans[$ - 10 .. $]);
  }
  
  try {
    for (; ; ) {
      N = readInt();
      S = new string[N];
      foreach (i; 0 .. N) {
        S[i] = readToken();
      }
      S.sort;
      if (N == ans.length) {
        writeln("NO");
      } else {
        foreach (i; 0 .. ans.length) {
          if (i >= N || ans[i] != S[i]) {
            writeln(ans[i]);
            break;
          }
        }
      }
    }
  } catch (EOFException e) {
  }
}