#include <bits/stdc++.h>
using namespace std;
#define all(c) (c).begin(),(c).end()
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;i--)
#define REP(i,m,n) for(int i=(int)(m);i<(int)(n);i++)
#define rep(i,n) REP(i,0,n)
#define iter(c) __typeof((c).begin())
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
#define mem(a) memset(a,0,sizeof(a))
#define pb(a) push_back(a)
#define in(a) insert(a)
#define R cin>>
#define F first
#define S second
#define C class
#define ll long long
#define ln cout<<'\n'
#define _(_1,_2,_3,N,...)N
#define pr(...) _(__VA_ARGS__,pr3,pr2,pr1)(__VA_ARGS__)
template<C T>void pr1(T a){cout<<a;ln;}
template<C T,C T2>void pr2(T a,T2 b){cout<<a<<' '<<b;ln;}
template<C T,C T2,C T3>void pr3(T a,T2 b,T3 c){cout<<a<<' '<<b<<' '<<c;ln;}
template<C T>void PR(T a,int n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
bool check(int n,int m,int x,int y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1000000007,MAXL=1LL<<60,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<int,int> P;


void Main() {
  int n;
  cin >> n;
  set<string> s;
  rep(i,n) {
    string t;
    cin >> t;
    s.in(t);
  }
  char a[6]={'a','a','i','u','u','e'};
  char b[5]={'n','b','m','g','r'};
  sort(a,a+6);
  sort(b,b+5);
  rep(i,6) {
    do {
      do {
	string t="";
	int k2=0;
	rep(k,6) {
	  if(i!=k) t+=b[k2++];
	  t+=a[k];
	}
	if(!s.count(t)) {
	  pr(t);
	  goto end;
	}
      } while(next_permutation(b,b+5));
    }while(next_permutation(a,a+6));
  }
  pr("NO");
 end:;
}

int main() {
  ios::sync_with_stdio(0);cin.tie(0);Main();
  return 0;
}