Time Limit : 2 Second
Memory Limit : 128 MB
Submission: 28
Solved: 12
 Description
 Farmer John has decided to give each of his cows a cell phone in
hopes to encourage their social interaction. This, however, requires
him to set up cell phone towers on his N (1 <= N <= 10,000) pastures
(conveniently numbered 1..N) so they can all communicate.
Exactly N1 pairs of pastures are adjacent, and for any two pastures
A and B (1 <= A <= N; 1 <= B <= N; A != B) there is a sequence of
adjacent pastures such that A is the first pasture in the sequence
and B is the last. Farmer John can only place cell phone towers in
the pastures, and each tower has enough range to provide service
to the pasture it is on and all pastures adjacent to the pasture
with the cell tower.
Help him determine the minimum number of towers he must install to
provide cell phone service to each pasture.
 Input
 * Line 1: A single integer: N
* Lines 2..N: Each line specifies a pair of adjacent pastures with two
spaceseparated integers: A and B
 Output
* Line 1: A single integer indicating the minimum number of towers to
install
 sample input

5
1 3
5 2
4 3
3 5
 sample output

2
 hint
 source
 USACO JAN08
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