n,*s = open(0).read().split()
s = set(s)
from itertools import permutations
print(s)
for b in permutations("aauuie"):
    for a in permutations("mgnbr"):
        for j in range(6):
            r = []
            c = 0
            for i in range(6):
                while c < i + (j <= i):
                    r.append(b[c])
                    c += 1
                if i < 5: r.append(a[i])
            if "".join(r) not in s:
                print("".join(r))
                exit()
print("NO")