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<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<queue>
using namespace std;
string S[500]; bool W[26][26]; int n;
vector<int>X[26];
bool SearchingHeiro(int m) {
	int dist[1000];
	for (int i = 0; i < m; i++) {
		queue<int>Q;
		for (int j = 0; j < m; j++)dist[j] = 0;
		Q.push(i); int cnt = 0;
		while (!Q.empty()) {
			cnt++; int a1 = Q.front(); Q.pop();
			if (cnt >= 100000) { return true; }
			for (int j = 0; j < X[a1].size(); j++) {
				if (dist[X[a1][j]] > dist[a1] - 1) {
					dist[X[a1][j]] = dist[a1] - 1;
					Q.push(X[a1][j]);
				}
			}
		}
	}
	return false;
}
bool solve() {
	for (int i = 0; i < 676; i++) { X[i / 26].clear(); W[i / 26][i % 26] = false; }
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			int Y = min(S[i].size(), S[j].size());
			for (int k = 0; k < Y + 1; k++) {
				if (k == Y) {
					if (S[i].size() > S[j].size())return false;
					break;
				}
				if (S[i][k] > S[j][k]) { W[S[i][k] - 'a'][S[j][k] - 'a'] = true; break; }
				if (S[i][k] < S[j][k]) { W[S[i][k] - 'a'][S[j][k] - 'a'] = true; break; }
			}
		}
	}
	for (int i = 0; i < 26; i++) {
		for (int j = 0; j < 26; j++) {
			if (W[i][j] == true)X[i].push_back(j);
		}
	}
	if (SearchingHeiro(26) == true)return false;
	return true;
}
int main() {
	while (true) {
		cin >> n; if (n == 0)break;
		for (int i = 0; i < n; i++)cin >> S[i];
		bool ans = solve();
		if (ans == true)cout << "yes" << endl;
		if (ans == false)cout << "no" << endl;
	}
	return 0;
}