Problem: There are n cities and n - 1 roads in the Seven Kingdoms, each road connects two cities and we can reach any city from any other by the roads.

Theon and Yara Greyjoy are on a horse in the first city, they are starting traveling through the roads. But the weather is foggy, so they can’t see where the horse brings them. When the horse reaches a city (including the first one), it goes to one of the cities connected to the current city. But it is a strange horse, it only goes to cities in which they weren't before. In each such city, the horse goes with equal probabilities and it stops when there are no such cities. 

Let the length of each road be 1. The journey starts in the city 1. What is the expected length (expected value of length) of their journey? You can read about expected (average) value by the link <https://en.wikipedia.org/wiki/Expected_value>.

Input

The first line contains a single integer n (1 ≤ n ≤ 100000) — number of cities.

Then n - 1 lines follow. The i-th line of these lines contains two integers ui and vi (1 ≤ ui, vi ≤ n, ui ≠ vi) — the cities connected by the i-th road.

It is guaranteed that one can reach any city from any other by the roads.

Output

Print a number — the expected length of their journey. The journey starts in the city 1.

Your answer will be considered correct if its absolute or relative error does not exceed 10 - 6.

Namely: let's assume that your answer is a, and the answer of the jury is b. The checker program will consider your answer correct, if <image>.

Examples

Input

4
1 2
1 3
2 4


Output

1.500000000000000


Input

5
1 2
1 3
3 4
2 5


Output

2.000000000000000

Note

In the first sample, their journey may end in cities 3 or 4 with equal probability. The distance to city 3 is 1 and to city 4 is 2, so the expected length is 1.5.

In the second sample, their journey may end in city 4 or 5. The distance to the both cities is 2, so the expected length is 2.

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class C {

  private static final String REGEX = " ";
  private static final Boolean DEBUG = false;
  private static final String FILE_NAME = "input.txt";


  public static void main(String[] args) throws IOException {
    if (DEBUG) {
      generate();
    }
    Solver solver = new Solver();
    solver.readData();
    solver.solve();
    solver.print();
  }

  private static void generate() throws IOException {
    FileWriter writer = new FileWriter("input.txt");
    writer.write("100000");
    writer.write("\n");
    for (int i = 0; i < 99999; i++) {
      writer.write(i + 1 + "");
      writer.write(" ");
      writer.write(i + 2 + "");
      writer.write("\n");
    }
    writer.close();
  }

  private static class Solver {
    private StringBuilder myStringBuilder = new StringBuilder();
    int n;
    Map<Integer, Set<Integer>> edges = new HashMap<>();
    double[] multResult;
    int[] distResult;

    void readData() throws IOException {
      Scanner scanner = new Scanner();
      n = scanner.nextInt();
      int source;
      int target;
      for (int i = 1; i <= n; i++) {
        edges.putIfAbsent(i, new HashSet<>());
      }
      multResult = new double[n + 1];
      distResult = new int[n + 1];
      for (int i = 0; i < n - 1; i++) {
        source = scanner.nextInt();
        target = scanner.nextInt();
        edges.get(source).add(target);
        edges.get(target).add(source);
      }
      scanner.close();
    }

    void solve() {
      Deque<Integer> vertexStack = new ArrayDeque<>(n);
      Deque<Double> multStack = new ArrayDeque<>(n);
      Deque<Integer> distStack = new ArrayDeque<>(n);
      vertexStack.add(1);
      multStack.add(1.0);
      distStack.add(0);
      boolean[] visited = new boolean[n+1];
      while (!vertexStack.isEmpty()) {
        Integer next = vertexStack.pop();
        Double mult = multStack.pop();
        Integer dist = distStack.pop();
        visited[next] = true;
        List<Integer> list = edges.get(next).stream().filter(it -> !visited[it]).collect(Collectors.toList());
        long count = list.size();
        if (count == 0) {
          multResult[next] = mult;
          distResult[next] = dist;
        } else {
          double newMult = mult / (double) count;
          list.forEach(vertex -> {
            vertexStack.push(vertex);
            multStack.push(newMult);
            distStack.push(dist + 1);
          });
        }
      }
      double result = 0.0;
      for (int i = 0; i <= n; i++) {
        result += multResult[i] * distResult[i];
      }
      out(result);
    }


    void print() {
      System.out.println(myStringBuilder);
    }


    void out(Object object) {
      myStringBuilder.append(object);
    }

    void out(String string) {
      myStringBuilder.append(string);
    }

    public void out(boolean b) {
      myStringBuilder.append(b);
    }

    public void out(char c) {
      myStringBuilder.append(c);
    }

    public void out(int i) {
      myStringBuilder.append(i);
    }

    public void out(long lng) {
      myStringBuilder.append(lng);
    }

    public void out(float f) {
      myStringBuilder.append(f);
    }

    public void out(double d) {
      myStringBuilder.append(d);
    }

    public void newLine() {
      myStringBuilder.append("\n");
    }

    @SuppressWarnings("SameParameterValue")
    int[] splitInteger(String string, int n) {
      final String[] split = string.split(REGEX, n);
      int[] result = new int[split.length];
      for (int i = 1; i <= n; ++i) {
        result[i] = Integer.parseInt(split[i]);
      }
      return result;
    }

    public int[] splitInteger(String string) {
      return splitInteger(string, 0);
    }


    @SuppressWarnings("SameParameterValue")
    long[] splitLong(String string, int n) {
      final String[] split = string.split(REGEX, n);
      long[] result = new long[split.length];
      for (int i = 0; i < n; ++i) {
        result[i] = Long.parseLong(split[i]);
      }
      return result;
    }

    public long[] splitLong(String string) {
      return splitLong(string, 0);
    }

    @SuppressWarnings("SameParameterValue")
    double[] splitDouble(String string, int n) {
      final String[] split = string.split(REGEX, n);
      double[] result = new double[split.length];
      for (int i = 0; i < n; ++i) {
        result[i] = Double.parseDouble(split[i]);
      }
      return result;
    }

    public double[] splitDouble(String string) {
      return splitDouble(string, 0);
    }

    @SuppressWarnings("SameParameterValue")
    String[] splitString(String string, int n) {
      return string.split(REGEX, n);
    }

    public String[] splitString(String string) {
      return splitString(string, 0);
    }

    public int max(int a, int b) {
      return Math.max(a, b);
    }

    public int max(int[] arr) {
      int max = Integer.MIN_VALUE;
      for (int x : arr) {
        max = max(max, x);
      }
      return max;
    }

    public long max(long a, long b) {
      return Math.max(a, b);
    }

    public int min(int a, int b) {
      return Math.min(a, b);
    }

    public long min(long a, long b) {
      return Math.min(a, b);
    }

    public double max(double a, double b) {
      return Math.max(a, b);
    }

    public double min(double a, double b) {
      return Math.min(a, b);
    }

    private final static int MOD = 1000000009;

    int multMod(int a, int b) {
      return ((a % MOD) * (b % MOD)) % MOD;
    }

    int sumMod(int a, int b) {
      return ((a % MOD) + (b % MOD)) % MOD;
    }

    long multMod(long a, long b) {
      return ((a % MOD) * (b % MOD)) % MOD;
    }

    long sumMod(long a, long b) {
      return ((a % MOD) + (b % MOD)) % MOD;
    }

  }

  private static class Scanner {
    private int currentIndex = 0;
    private String[] objects;
    private final BufferedReader myReader;
    private Computable<Character> charComputer;
    private Computable<Double> doubleComputer;
    private Computable<Integer> intComputer;
    private Computable<Long> longComputer;

    Scanner() throws FileNotFoundException {
      InputStream in = DEBUG ? new FileInputStream(FILE_NAME) : System.in;
      myReader = new BufferedReader(new InputStreamReader(in));
      charComputer = () -> objects[currentIndex].charAt(0);
      doubleComputer = () -> Double.parseDouble(objects[currentIndex]);
      intComputer = () -> Integer.parseInt(objects[currentIndex]);
      longComputer = () -> Long.parseLong(objects[currentIndex]);
    }

    String nextLine() throws IOException {
      objects = null;
      currentIndex = 0;
      return myReader.readLine();
    }

    int nextInt() throws IOException {
      return next(intComputer);

    }

    long nextLong() throws IOException {
      return next(longComputer);

    }

    double nextDouble() throws IOException {
      return next(doubleComputer);

    }

    char nextChar() throws IOException {
      return next(charComputer);
    }

    <T> T next(Computable<T> computer) throws IOException {
      T result;
      if (objects == null || currentIndex >= objects.length) {
        String s = myReader.readLine();
        objects = s.split(" ");
        currentIndex = 0;
      }
      result = computer.compute();
      currentIndex++;
      return result;
    }

    interface Computable<T> {
      T compute();
    }

    public void close() throws IOException {
      myReader.close();
    }
  }

}