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<bits/stdc++.h>
#define f first
#define s second
#define mp make_pair
using namespace std;

int n;
string s[501],ans;
vector<int> v[28];
bool visited[28],checked[28];

void init(){
  for(int i=0;i<28;i++){
    v[i].clear();
    visited[i]=false;
    checked[i]=false;
  }
}

pair<char,char> func(string a,string b){
  pair<char,char> pcc;
  a+='A';b+='A';
  for(int i=0;i<a.length();i++){
    if(a[i]!=b[i]){
      pcc.f=a[i];
      pcc.s=b[i];
      break;
    }
  }
  return pcc;
}

void dfs(int num){
  if(visited[num]){
    ans="no";
    return;
  }
  visited[num]=true;
  for(int i=0;i<v[num].size();i++){
    if(!checked[v[num][i]])dfs(v[num][i]);
  }
  checked[num]=true;
  visited[num]=false;
}

int main()
{

  while(1){
    cin>>n;
    if(n==0)break;
    init();
    for(int i=0;i<n;i++)cin>>s[i];
    ans="yes";
    for(int i=0;i<n;i++){
      for(int j=i+1;j<n;j++){
	if(s[i]==s[j])continue;
	pair<char,char> pcc=func(s[i],s[j]);
	int a,b;
	if(pcc.f=='A')a=27;
	else a=pcc.f-'a';
	if(pcc.s=='A')b=27;
	else b=pcc.s-'a';
	if(b==27)ans="no";
	v[a].push_back(b);
      }
    }

    for(int i=0;i<28;i++){
      if(!checked[i])dfs(i);
    }
    cout<<ans<<endl;
  }
  return 0;
}