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
#define _USE_MATH_DEFINES
#define INF 0x3f3f3f3f

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <queue>
#include <stack>
#include <limits>
#include <map>
#include <string>
#include <cstring>
#include <set>
#include <deque>
#include <bitset>
#include <list>
#include <cctype>
#include <utility>
  
using namespace std;
  
typedef long long ll;
typedef pair <string,int> P;
typedef pair <int,P> PP;
  
static const double EPS = 1e-8;
  
const static int tx[] = {0,1,0,-1};
const static int ty[] = {-1,0,1,0};

int main(){
  int N;
  while(~scanf("%d",&N)){
    if(N == 0) break;
    vector<string> dict;
    int prior[256][256]; // prior[A][B] ::= A is prior to B or not
    memset(prior,-1,sizeof(prior));

    bool isok = true;
    bool res = true;
    for(int current_idx=0;current_idx<N;current_idx++){
      string current;
      cin >> current;

      for(int prev_idx=0;prev_idx<dict.size();prev_idx++){
        for(int char_idx=0;
            char_idx < current.size() && char_idx < dict[prev_idx].size();
            char_idx++){
          if(current[char_idx] == dict[prev_idx][char_idx]) continue;

          if(prior[dict[prev_idx][char_idx]][current[char_idx]] == 1){
            break;
          }

          if(prior[dict[prev_idx][char_idx]][current[char_idx]] == -1){
            prior[dict[prev_idx][char_idx]][current[char_idx]] = 1;
            prior[current[char_idx]][dict[prev_idx][char_idx]] = 0;
            break;
          }
        }

        bool isok = true;
        bool is_first = true;
        for(int char_idx=0;
            char_idx < current.size() && char_idx < dict[prev_idx].size();
            char_idx++){
          if(current[char_idx] == dict[prev_idx][char_idx]) continue;
          if(is_first && prior[current[char_idx]][dict[prev_idx][char_idx]] == 1){
            isok = false;
            break;
          }
          is_first = false;
        }

        if(isok){
          if(current.size() < dict[prev_idx].size()
             && dict[prev_idx].substr(0,current.size()) == current){
            isok = false;
          }
        }

        res &= isok;
      }

      dict.push_back(current);
    }
  found:;
    printf("%s\n",res ? "yes" : "no");
  }
}