from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
# input = sys.stdin.readline

N = int(input())
S = set([input() for _ in range(N)])
X = list('inabameguru')
A = X[0::2]
B = X[1::2]
n = len(B)
for pa in permutations(A):
    for pb in permutations(B):
        ans = pa[0]
        for i in range(n):
            ans += pb[i] + pa[i+1]
        if ans in S:
            continue
        print(ans)
        exit()
print('NO')