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mn/690-F1
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# Tree of Life (easy) Heidi has finally found the mythical Tree of Life - a legendary combinatorial structure which is said to contain a prophecy crucially needed to defeat the undead armies. On the surface, the Tree of Life is just a regular undirected tree well-known from computer science. This means that it is a collection of $n$ points (called vertices), some of which are connected using $n - 1$ line segments (edges) so that each pair of vertices is connected by a path$ (a sequence of one or more edges). To decipher the prophecy, Heidi needs to perform a number of steps. The first is counting the number of lifelines$ in the tree - these are paths of length $2$, i.e., consisting of two edges. Help her! ## Оролт The first line of the input contains a single integer $n$ - the number of vertices in the tree ($1 ≤ n ≤ 10000$). The vertices are labeled with the numbers from 1 to $n$. Then $n - 1$ lines follow, each describing one edge using two space-separated numbers $a b$ - the labels of the vertices connected by the edge ($1 ≤ a < b ≤ n$). It is guaranteed that the input represents a tree. ## Гаралт Print one integer - the number of lifelines in the tree. ## Тэмдэглэл In the second sample, there are four lifelines: paths between vertices $1$ and $3$, $2$ and $4$, $2$ and $5$, and $4$ and $5$. -- [орчуулагдаж байгаа]
Жишээ тэстүүд
Оролт
4 1 2 1 3 1 4
Гаралт
3
Оролт
5 1 2 2 3 3 4 3 5
Гаралт
4
Тэмдэглэл