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>

#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

int main(){
	for(int n;scanf("%d",&n),n;){
		char s[500][11];
		rep(i,n) scanf("%s",s[i]);

		bool ok=true;
		bool adj[26][26]={};
		rep(i,n-1){
			for(int j=0;;j++){
				if(s[i][j]=='\0') break;
				if(s[i+1][j]=='\0'){ ok=false; break; }
				if(s[i][j]!=s[i+1][j]){
					adj[s[i][j]-'a'][s[i+1][j]-'a']=true;
					break;
				}
			}
		}
		rep(k,26) rep(i,26) rep(j,26) adj[i][j]|=adj[i][k]&&adj[k][j];

		rep(i,26) if(adj[i][i]) ok=false;
		puts(ok?"yes":"no");
	}

	return 0;
}