HDU4612 Warm up

Time Limit: 5000MS

Memory Limit: 65535KB

64bit IO Format: %I64d & %I64u

Description

　　N planets are connected by M bidirectional channels that allow instant transportation. It's always possible to travel between any two planets through these channels. 
　　If we can isolate some planets from others by breaking only one channel , the channel is called a bridge of the transportation system. 
People don't like to be isolated. So they ask what's the minimal number of bridges they can have if they decide to build a new channel. 
　　Note that there could be more than one channel between two planets. 

Input

　　The input contains multiple cases. 
　　Each case starts with two positive integers N and M , indicating the number of planets and the number of channels. 
　　(2<=N<=200000, 1<=M<=1000000) 
　　Next M lines each contains two positive integers A and B, indicating a channel between planet A and B in the system. Planets are numbered by 1..N. 
　　A line with two integers '0' terminates the input.

Output

　　For each case, output the minimal number of bridges after building a new channel in a line.

Sample Input

4 4
1 2
1 3
1 4
2 3
0 0 

Sample Output

0

Source

2013 Multi-University Training Contest 2

 

在原图上任意加一条边，询问最少还剩下多少桥。

缩完点，找树直径，把直径两端连起来，就是最优策略。