A14961 | Towers

You are given a tree with $n$ vertices numbered from $1$ to $n$ . The height of the $i$ -th vertex is $h_i$ . You can place any number of towers into vertices, for each tower you can choose which vertex to put it in, as well as choose its efficiency. Setting up a tower with efficiency $e$ costs $e$ coins, where $e > 0$ .

It is considered that a vertex $x$ gets a signal if for some pair of towers at the vertices $u$ and $v$ ( $u \neq v$ , but it is allowed that $x = u$ or $x = v$ ) with efficiencies $e_u$ and $e_v$ , respectively, it is satisfied that $\min(e_u, e_v) \geq h_x$ and $x$ lies on the path between $u$ and $v$ .

Find the minimum number of coins required to set up towers so that you can get a signal at all vertices.

The first line contains an integer $n$ ( $2 \le n \le 200\,000$ ) — the number of vertices in the tree.

The second line contains $n$ integers $h_i$ ( $1 \le h_i \le 10^9$ ) — the heights of the vertices.

Each of the next $n - 1$ lines contain a pair of numbers $v_i, u_i$ ( $1 \le v_i, u_i \le n$ ) — an edge of the tree. It is guaranteed that the given edges form a tree.

Print one integer — the minimum required number of coins.