Red Hood

import java.util.*;


public class Main {
    static Map<Integer, Vertex> distances = new HashMap<>();
    static int max = 0;
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();
        List<Vertex> vertices = new ArrayList<>();
        List<Vertex> leaves = new ArrayList<>();
        for (int i = 0; i < N; i++) {
            Vertex current = new Vertex(in.nextInt());
            vertices.add(current);
            leaves.add(current);
        }
        for (int i = 0; i < N - 1; i++) {
            Vertex one = vertices.get(in.nextInt() - 1);
            Vertex two = vertices.get(in.nextInt() - 1);
            one.addLink(two);
            two.addLink(one);
            if (one.getLinks() > 1) {
                leaves.remove(one);
            }
            if (two.getLinks() > 1) {
                leaves.remove(two);
            }
        }

        dfs(leaves.get(0), null, leaves.get(0).value);

        Vertex start = distances.get(max);
        dfs(start, null, start.value);
        System.out.println(max);

    }

    private static void dfs(Vertex vertex, Vertex parent, int distance) {
        List<Vertex> links = vertex.links;
        for (Vertex link :
                links) {
            if (link.equals(parent)){
                distances.put(distance, vertex);
                max = Math.max(max, distance);
                continue;
            }
            dfs(link, vertex, distance + link.value);
        }

    }

    static class Vertex{
        List<Vertex> links = new ArrayList<>();
        int value;

        public Vertex(){
        }
        public Vertex(int value){
            setValue(value);
        }

        void setValue(int value){
            this.value = value;
        }

        void addLink(Vertex link){
            links.add(link);
        }

        int getLinks(){
            return links.size();
        }
    }
}