#include <bits/stdc++.h>
using namespace std;

#define lp(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) lp(i, 0, n)
#define rlp(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define rrep(i, n) rlp(i, 0, n)

#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(c) begin(c), end(c)

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pr;
typedef tuple<int, int, int> tp;

template<typename T>
inline bool chmin(T &a, T b){
	if (a <= b) return false;
	a = b; return true;
}

template<typename T>
inline bool chmax(T &a, T b){
	if (a >= b) return false;
	a = b; return true;
}

template<typename T>
inline void unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
}

template<typename T>
inline T sq(T a){
	return a * a;
}

int n;
set<string> st;

int main()
{
	cin >> n;
	rep(i, n){
		string s;
		cin >> s;
		st.insert(s);
	}

	string s, t;
	rep(i, 11) (i & 1 ? t : s) += "inabameguru"[i];
	sort(all(s)); sort(all(t));
	
	string res = "NO";
	do {
		do {
			string u;
			rep(i, 11) u += (i & 1 ? t : s)[i / 2];
			if (!st.count(u)) res = u;
		} while (next_permutation(all(t)));
	} while (next_permutation(all(s)));

	cout << res << endl;
}