Problem Statement

We found a dictionary of the Ancient Civilization Mayo (ACM) during excavation of the ruins. After analysis of the dictionary, we revealed they used a language that had not more than 26 letters. So one of us mapped each letter to a different English alphabet and typed all the words in the dictionary into a computer.

How the words are ordered in the dictionary, especially whether they are ordered lexicographically, is an interesting topic to many people. As a good programmer, you are requested to write a program to judge whether we can consider the words to be sorted in a lexicographical order.

Note: In a lexicographical order, a word always precedes other words it is a prefix of. For example, `ab` precedes `abc`, `abde`, and so on.



Input

The input consists of multiple datasets. Each dataset is formatted as follows:


n
string_1
...
string_n


Each dataset consists of n+1 lines. The first line of each dataset contains an integer that indicates n (1 \leq n \leq 500). The i-th line of the following n lines contains string_i, which consists of up to 10 English lowercase letters.

The end of the input is `0`, and this should not be processed.

Output

Print either `yes` or `no` in a line for each dataset, in the order of the input. If all words in the dataset can be considered to be ordered lexicographically, print `yes`. Otherwise, print `no`.

Example

Input

4
cba
cab
b
a
3
bca
ab
a
5
abc
acb
b
c
c
5
abc
acb
c
b
b
0


Output

yes
no
yes
no
#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<queue>

using namespace std;

#define int long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define INF (long long)(1e18)
#define MOD (int)(1e9+7)

#define yn(f) ((f)?"yes":"no")
#define YN(f) ((f)?"YES":"NO")

#define MAX 510

string s[MAX];
bool temp[30][30];
int ans;

void fuga(int a, int b){//cout<<(char)(a+'a')<<" "<<(char)(b+'a')<<endl;
	if(a==b||!ans) return;
	temp[a][b] = true;
	if(temp[a][b]&&temp[b][a]){
		ans = false;
		//cout<<"XXXX "<<(char)(a+'a')<<" "<<(char)(b+'a')<<endl;
	}
}

void hogehoge(int a, int b){
	if(a==b||!ans)return;
	
	queue<int> Q;
	bool used[30] = {};
	Q.push(a);
	
	while(!Q.empty()){
		int t = Q.front();Q.pop();
		used[t] = true;//cout<<t<<endl;
		fuga(t,b);
		for(int i = 0 ; i < 26; i++){
			if(!used[i]&&temp[i][t]) Q.push(i);
		}
	}
}

void hoge(string a, string b){
	if(!ans) return;
	int flag = 1;
	for(int i = 0,size = min(a.size(),b.size()); i < size; i++){//cout<<i<<"---"<<endl;
		if(flag)hogehoge(a[i]-'a',b[i]-'a');
		if(a[i] != b[i]) flag = false;
	}
	if(flag&&b.size()<a.size())ans = false;
}

signed main(){
	cout<<fixed<<setprecision(7);
	
	
	while(true){
		int n;
		
		ans = true;
		rep(i,30)rep(j,30)temp[i][j]=false;
		
		cin>>n;
		
		if(!n) break;
		
		for(int i = 0; i < n; i++){
			cin>>s[i];
			if(i) hoge(s[i-1],s[i]);
	}
	
		cout<<yn(ans)<<endl;
	}
	
	return 0;
}
