p1985_CowMarathon

Cow Marathon

Time Limit: 2000MS		Memory Limit: 30000K
Total Submissions: 1290		Accepted: 570
Case Time Limit: 1000MS

Description

After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has committed to create a bovine marathon for his cows to run. The marathon route will include a pair of farms and a path comprised of a sequence of roads between them. Since FJ wants the cows to get as much exercise as possible he wants to find the two farms on his map that are the farthest apart from each other (distance being measured in terms of total length of road on the path between the two farms). Help him determine the distances between this farthest pair of farms.

Input

* Lines 1.....: Same input format as "Navigation Nightmare".

Output

* Line 1: An integer giving the distance between the farthest pair of farms.

Sample Input

7 6

1 6 13 E

6 3 9 E

3 5 7 S

4 1 3 N

2 4 20 W

4 7 2 S

Sample Output

52

Hint

The longest marathon runs from farm 2 via roads 4, 1, 6 and 3 to farm 5 and is of length 20+3+13+9+7=52.

Source

USACO 2004 February

题目大意： 在一颗树上找到两个点的距离的最大值。 就是经典的树形dp，不过调试了多久呢，将近两天，是一个小错误，看了很久就是没发现，重新写了一下以前的代码才突然想到的。。。 这样的效率不好！一鼓作气！