## 题目描述

A company offers personal computers for sale in N towns ( 3<=N<=35), denoted by 1, 2,…, N. There are direct routes connecting M pairs among these towns. The company decides to build servicing stations to ensure that for any town X, there will be a station located either in X or in some immediately neighboring town of X. Write a program to find the minimum number of stations the company has to build.

## 输入

The input consists of multiple problem descriptions. Every description starts with number of towns N and number of town-pairs M, separated by a space. Each of the next M lines contains a pair of integers representing connected towns, at one pair per line with each pair separated by a space. The input ends with N = 0 and M = 0.

## 输出

For each input case, print a line reporting the minimum number of servicing stations needed.

## 样例输入

```
8 12
1 2
1 6
1 8
2 3
2 6
3 4
3 5
4 5
4 7
5 6
6 7
6 8
0 0
```

## 样例输出

```
2
```

## 参考代码

```
暂无
```

## 解析

暂无