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<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<iostream>
#include<queue>
#include<stack>
#include<vector>
#include<map>
#include<set>
#include<string>
using namespace std;
#define INF 0x3f3f3f3f
#define eps 1e-8
#define maxn 100005
#define mod 1000000009

char s[505][15];
vector<int>g[30];
int deg[30];
bool v[30];
void topo()
{
    queue<int>q;
    for(int i=0;i<26;i++)   if(deg[i]==0)   q.push(i);
    int all=0;
    while(!q.empty())
    {
        int now=q.front();
        if(v[now]==1)
        {
            q.pop();
            continue;
        }
        v[now]=1;
        all++;
        q.pop();
        for(int i=0;i<g[now].size();i++)
        {
            int temp=g[now][i];
            deg[temp]--;
            if(deg[temp]==0)    q.push(temp);
        }
    }
    if(all==26) printf("yes\n");
    else printf("no\n");
}
int main()
{
    while(1)
    {
        int n;
        scanf("%d",&n);
        if(n==0)    break;
        bool flag=0;
        for(int i=0;i<26;i++)   g[i].clear();
        for(int i=0;i<26;i++)
        {
            deg[i]=0;
            v[i]=0;
        }
        for(int i=0;i<n;i++)
        {
            scanf("%s",s[i]);
        }
        for(int i=0;i<n;i++)
        {
            for(int j=i+1;j<n;j++)
            {
                int leni=strlen(s[i]),lenj=strlen(s[j]);
                bool sign=0;
                for(int k=0;k<min(leni,lenj);k++)
                {
                    if(s[i][k]!=s[j][k])
                    {
                        g[s[i][k]-'a'].push_back(s[j][k]-'a');
                        deg[s[j][k]-'a']++;
                        sign=1;
                        break;
                    }
                }
                if(sign==0)
                {
                    if(leni>lenj)
                    {
                        flag=1;
                        break;
                    }
                }
            }
            if(flag==1) break;
        }
        if(flag==1) printf("no\n");
        else topo();

    }
}