#2060. [Usaco2010 Nov]Visiting Cows 拜访奶牛

题目描述

经过了几周的辛苦工作,贝茜终于迎来了一个假期.作为奶牛群中最会社交的牛,她希望去拜访N(1<=N<=50000)个朋友.这些朋友被标号为1..N.这些奶牛有一个不同寻常的交通系统,里面有N-1条路,每条路连接了一对编号为C1和C2的奶牛(1 <= C1 <= N; 1 <= C2 <= N; C1<>C2).这样,在每一对奶牛之间都有一条唯一的通路. FJ希望贝茜尽快的回到农场.于是,他就指示贝茜,如果对于一条路直接相连的两个奶牛,贝茜只能拜访其中的一个.当然,贝茜希望她的假期越长越好,所以她想知道她可以拜访的奶牛的最大数目.

输入格式

第1行:单独的一个整数N 第2..N行:每一行两个整数,代表了一条路的C1和C2.

输出格式

单独的一个整数,代表了贝茜可以拜访的奶牛的最大数目.

样例

样例输入

7  

6 2  

3 4  

2 3  

1 2  

7 6  

5 6  

  

  

INPUT DETAILS:  

  

Bessie knows 7 cows. Cows 6 and 2 are directly connected by a road,  

as are cows 3 and 4, cows 2 and 3, etc. The illustration below depicts the  

roads that connect the cows:  

  

                       1--2--3--4  

                          |  

                       5--6--7  

样例输出

4  

  

OUTPUT DETAILS:  

  

Bessie can visit four cows. The best combinations include two cows  

on the top row and two on the bottom. She can't visit cow 6 since  

that would preclude visiting cows 5 and 7; thus she visits 5 and  

7. She can also visit two cows on the top row: {1,3}, {1,4}, or  

{2,4}.  

数据范围与提示