#P2977. [USACO10JAN] Cow Telephones G
[USACO10JAN] Cow Telephones G
Description
The cows have set up a telephone network, which for the purposes of this problem can be considered to be an unrooted tree of unspecified degree with () vertices conveniently numbered . Each vertex represents a telephone switchboard, and each edge represents a telephone wire between two switchboards. Edge is specified by two integers and the are the two vertices joined by edge (; ; ).
Some switchboards have only one telephone wire connecting them to another switchboard; these are the leaves of the tree, each of which is a telephone booth located in a cow field.
For two cows to communicate, their conversation passes along the unique shortest path between the two vertices where the cows are located. A switchboard can accomodate only up to () simultaneous conversations, and there can be at most one conversation going through a given wire at any one time.
Given that there is a cow at each leaf of the tree, what is the maximum number of pairs of cows that can simultaneously hold conversations? A cow can, of course, participate in at most one conversation.
Input Format
* Line : Two space separated integers: and .
* Lines : Line contains two space-separated integers: and .
Output Format
* Line : The number of pairs of cows that can simultaneously hold conversations.
6 1
1 2
2 3
2 4
4 5
4 6
2
Hint
1 5 C1 C5
| | || ||
2---4 --> |2---4|
| | || ||
3 6 C3 C6
Consider this six-node telephone tree with :
There are four cows, located at vertices , , and . If cow talks to cow , and cow talks to cow , then they do not exceed the maximum number of conversations per switchboard, so for this example the answer is (for two pairs of cows talking simultaneously).
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