import java.util.*;

public class Main {
    static char[] boin = new char[]{'i', 'a', 'a', 'e', 'u', 'u'};
    static char[] shiin = new char[]{'n', 'b', 'm', 'g', 'r'};
    static final int MAX = boin.length + shiin.length;
    static HashSet<String> ngs = new HashSet<>();
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            ngs.add(sc.next());
        }
        
        boolean[] bUsed = new boolean[boin.length];
        boolean[] sUsed = new boolean[shiin.length];
        addBoin(new char[MAX], bUsed, sUsed, 0, false);
        addShiin(new char[MAX], bUsed, sUsed, 0, true);
        System.out.println("NO");
    }
    
    static void addBoin(char[] arr, boolean[] bUsed, boolean[] sUsed, int count, boolean remain) {
        if (count == MAX) {
            if (!ngs.contains(new String(arr))) {
                System.out.println(arr);
                System.exit(0);
            }
            return;
        }
        for (int i = 0; i < boin.length; i++) {
            if (bUsed[i]) {
                continue;
            }
            bUsed[i] = true;
            arr[count] = boin[i];
            addShiin(arr, bUsed, sUsed, count + 1, remain);
            if (remain) {
                addBoin(arr, bUsed, sUsed, count + 1, false);
            }
            bUsed[i] = false;
        }
        
    }
    
    static void addShiin(char[] arr, boolean[] bUsed, boolean[] sUsed, int count, boolean remain) {
        if (count == MAX) {
            if (!ngs.contains(new String(arr))) {
                System.out.println(arr);
                System.exit(0);
            }
            return;
        }
        for (int i = 0; i < shiin.length; i++) {
            if (sUsed[i]) {
                continue;
            }
            sUsed[i] = true;
            arr[count] = shiin[i];
            addBoin(arr, bUsed, sUsed, count + 1, remain);
            sUsed[i] = false;
        }
    }
}