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;
const int MAXN=505;
char str[MAXN][15];
int in[26];
bool used[26][26];
int main(){
    int n, cnt;
    queue<int> q;
    while(cin>>n&&n){
        memset(in,0,sizeof in);
        memset(used,0,sizeof used);
        bool flag=true;
        for(int i=0; i<n; i++){
            scanf("%s",str[i]);
            int len=strlen(str[i]);
            if(i&&flag){
                for(int k=0; k<len; k++){
                    if(str[i][k]==str[i-1][k]){
                        continue;
                    }
                    if(!str[i][k]) goto ok;
                    int s1=str[i-1][k]-'a', s2=str[i][k]-'a';
//                    assert(s1>=0);assert(s2>=0);
                    if(used[s2][s1]) flag=false;
                    if(!used[s1][s2]){
                        used[s1][s2]=true;
                        in[s2]++;
                    }
                    goto ok;
                }
                if(str[i-1][len]) flag=false;
                ok:;
            }
        }
        if(!flag) goto failed;
        while(!q.empty()) q.pop();
        for(int i=0; i<26; i++){
            if(in[i]==0){
                q.push(i);
            }
        }
        cnt=0;
        while(!q.empty()){
            int now=q.front(); q.pop();
            for(int i=0; i<26; i++){
                if(used[now][i]){
                    in[i]--;
                    if(in[i]==0){
                        q.push(i);
                    }
                }
            }
            cnt++;
        }
        if(cnt!=26) goto failed;
        puts("yes");
        continue;
        failed:;
        puts("no");
    }
    return 0;
}