from itertools import permutations

N = input()
S = set([])
for i in xrange(N):
    S.add(raw_input())

# inabameguru
cons = list("nbmgr")
vow = list("iaaeuu")
for cs in permutations(cons):
    for vs in permutations(vow):
        base = []
        for i in xrange(len(cs)):
            base.append(cs[i])
            base.append(vs[i])
        for i in xrange(len(base)+1):
            name = base[:i] + [vs[5]] + base[i:]
            if ''.join(name) not in S:
                print(''.join(name))
                quit()
print('NO')