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<algorithm>
using namespace std;
int n,flg,t[26][26];
string str[500];
void check(int x,int y){
  //cout<<str[x]<<' '<<str[y]<<endl;
  int v = str[x].size();
  int w = str[y].size();
  for(int i=0;i<min(v,w);i++){
    if(str[x][i]==str[y][i])continue;
    if(t[str[x][i]-'a'][str[y][i]-'a']==-1)flg=0;
    t[str[x][i]-'a'][str[y][i]-'a']=1;
    t[str[y][i]-'a'][str[x][i]-'a']=-1;
    return;
  }
  if(w<v)flg=0;
}
int main(){
  while(cin>>n&&n){

    for(int i=0;i<26;i++)
      for(int j=0;j<26;j++)
	t[i][j]=0;

    flg=1;
    cin>>str[0];
    for(int i=1;i<n;i++){
      cin>>str[i];
      for(int j=i-1;j>=0;j--)check(j,i);
    }
    cout<<(flg?"yes":"no")<<endl;
  }
  return 0;
}