#include<iostream>
#include<set>
#include<vector>
#include<algorithm>
using namespace std;
main()
{
	set<string>S;
	vector<char>A={'a','a','e','i','u','u'};
	vector<char>B={'b','g','m','n','r'};
	do{
		do{
			string now="";
			for(int i=0;i<5;i++)now+=B[i],now+=A[i];
			for(int i=0;i<5;i++)
			{
				S.insert(now.substr(0,i*2)+A[5]+now.substr(i*2));
			}
		}while(next_permutation(B.begin(),B.end()));
	}while(next_permutation(A.begin(),A.end()));
	int N;
	cin>>N;
	for(;N--;)
	{
		string s;
		cin>>s;
		S.erase(s);
	}
	set<string>::iterator it=S.begin();
	cout<<(it==S.end()?"NO":*it)<<endl;
}