import itertools
boin=["i","a","a","e","u","u"]
siin=["n","b","m","g","r"]
N=int(raw_input())
S=[raw_input() for i in range(N)]
set(S)
for p in itertools.permutations(boin):
    for q in itertools.permutations(siin):
        for j in range(5):
            s=""
            for i in range(5):
                s+=q[i]
                s+=p[i]
                if i==j :
                    s+= p[5]
        if not (s in S):
            print s
            exit()
        s=p[5]
        for i in range(5):
            s+=q[i]
            s+=p[i]
        if not (s in S):
            print s
            exit()
print "NO"