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>
using namespace std;

#define REP(i, s, e) for(int i = (int)s; i < (int) e; i++)
#define rep(i, n) REP(i, 0 ,n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

#define fi first
#define se second


typedef long long ll;

int main(){
  int n;
  char s[1024][256];
  while(~scanf("%d", &n) && n){
        rep(i, n) scanf("%s", s[i]);
        set<char> st[256];
        bool ans = true;
        rep(i, n){
          REP(j, i+1, n){
                bool f = true;
                int li = strlen(s[i]), lj = strlen(s[j]);
                int l = min(li, lj);
                rep(k, l){
                  if(s[i][k] != s[j][k]){
                        f =false;
                        if(st[s[j][k]].count(s[i][k])){
                          ans = false;
                          break;
                        }
                        st[s[i][k]].insert(s[j][k]);
                        break;
                  }
                }
                if(f && li > lj) ans = false;
          }
        }
        printf("%s\n", (ans?"yes" : "no"));
  }
}