690F1 орчуулах · Codeforces.mn

# 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 $5$.

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