from itertools import permutations

X=list(permutations("nbmgr"))
Y=list(permutations("iaaeuu"))


S=set()

for x in X:
    for y in Y:
        A=[]

        for i in range(5):
            A.append(x[i])
            A.append(y[i])

        for i in range(len(A)):
            S.add("".join(A[:i]+[y[-1]]+A[i:]))

N=int(input())
LIST=set([input() for i in range(N)])

if len(LIST)==len(S):
    print("NO")
else:
    for s in S:
        if s in LIST:
            pass
        else:
            print(s)
            break