Tree

import java.io.*;
import java.util.*;

public class Tree {
    FastScanner in;
    PrintWriter out;

    class Dsu {
        int[] p;

        Dsu(int n) {
            p = new int[n];
            for (int i = 0; i < n; i++) {
                p[i] = i;
            }
        }

        int get(int v) {
            return p[v] == v ? v : (p[v] = get(p[v]));
        }

        void unite(int x, int y) {
            p[get(x)] = get(y);
        }
    }

    double sum;

    int go(int v, int p, int curH, ArrayList<Integer>[] g) {
        int maxH = curH;
        for (int to : g[v]) {
            if (to != p) {
                maxH = Math.max(maxH, go(to, v, curH + 1, g));
            }
        }
        sum += curH * 1.0 * (maxH - curH);
        return maxH;
    }

    void solve() {
        Random rnd = new Random(123);
        for (int it = 0; it < 50; it++) {
            int n = 30_000;
            Dsu dsu = new Dsu(n);
            ArrayList<Integer>[] g = new ArrayList[n];
            for (int i = 0; i < n; i++) {
                g[i] = new ArrayList<>();
            }
            for (int iter = 0; iter < n - 1; iter++) {
                int x = rnd.nextInt(n);
                int y = rnd.nextInt(n);
                if (dsu.get(x) != dsu.get(y)) {
                    g[x].add(y);
                    g[y].add(x);
                    dsu.unite(x, y);
                } else {
                    iter--;
                }
            }
            sum = 0;
            go(0, 0, 1, g);
            System.err.println("avarage = " + sum / n);
        }
    }

    void run() {
        try {
            in = new FastScanner(new File("tree.in"));
            out = new PrintWriter(new File("tree.out"));

            solve();

            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }

    void runIO() {

        in = new FastScanner(System.in);
        out = new PrintWriter(System.out);

        solve();

        out.close();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        public FastScanner(InputStream f) {
            br = new BufferedReader(new InputStreamReader(f));
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return null;
                st = new StringTokenizer(s);
            }
            return st.nextToken();
        }

        boolean hasMoreTokens() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return false;
                st = new StringTokenizer(s);
            }
            return true;
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }
    }

    public static void main(String[] args) {
        new Tree().runIO();
    }
}