#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<cctype>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())




int main(){
	string str("inabameguru");
	int n;
	cin>>n;
	vector<string> s(n);
	rep(i,n)cin>>s[i];
	sort(all(str));
	do{
		bool ok=true;
		rep(i,str.size()-1){
			if(isupper(str[i])&&isupper(str[i+1]))ok=false;
		}
		if(isupper(str[str.size()-1]))ok=false;
		if(ok&&!binary_search(all(s),str)){
			cout<<str<<endl;
			return 0;
		}
	}while(next_permutation(all(str)));
	cout<<"NO"<<endl;
	return 0;
}