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.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.StringTokenizer;

public class Main {
    
    public static void main(String[] args) throws UnsupportedEncodingException, IOException {
        Reader.init(System.in);
        StringBuilder out = new StringBuilder();
        int n = Reader.nextInt();
        Graph g = new Graph(n);
        while(--n > 0)
            g.addEdge(Reader.nextInt(), Reader.nextInt());
        Queue<Vertex> q = new LinkedList<Vertex>();
        q.add(g.vertexArray[1]);
        g.vertexArray[1].e = 1.0;
        Vertex v;
        double e = 0.0;
        int cnt;
        while(!q.isEmpty()) {
            v = q.poll();
            v.visited = true;
            cnt = v.edges.size();
            for(Vertex vv : v.edges)
                if(vv.visited)
                    cnt--;
            for(Vertex vv : v.edges)
                if(!vv.visited) {
                    vv.e = 1.0 / (double) cnt * v.e;
                    e += vv.e;
                    q.add(vv);
                }
        }
        out.append(e).append('\n');
        PrintWriter p = new PrintWriter(System.out);
        p.print(out);
        p.close();
    }
    
}

class Vertex {
    
    boolean visited;
    double e;
    List<Vertex> edges;
    
    public Vertex() {
        edges = new LinkedList<Vertex>();
    }
    
}

class Graph {
    
    Vertex[] vertexArray;
    
    public Graph(int size) {
            vertexArray = new Vertex[size + 1];
            for(int i = 1; i <= size; i++)
                vertexArray[i] = new Vertex();
    }
    
    public void addEdge(int v1, int v2) {
        vertexArray[v1].edges.add(vertexArray[v2]);
        vertexArray[v2].edges.add(vertexArray[v1]);
    }
    
}

class Reader {
    static BufferedReader reader;
    static StringTokenizer tokenizer;

    /** call this method to initialize reader for InputStream */
    static void init(InputStream input) throws UnsupportedEncodingException {
        reader = new BufferedReader(
                     new InputStreamReader(input, "UTF-8") );
        tokenizer = new StringTokenizer("");
    }
    
    static void init(String fileUrl) throws UnsupportedEncodingException, FileNotFoundException {
        reader = new BufferedReader(new FileReader(fileUrl));
        tokenizer = new StringTokenizer("");
    }

    /** get next word */
    static String next() throws IOException {
        while ( ! tokenizer.hasMoreTokens() ) {
            //TODO add check for eof if necessary
            tokenizer = new StringTokenizer(
                   reader.readLine() );
        }
        return tokenizer.nextToken();
    }
    
    static String nextLine() throws IOException {
        return reader.readLine();
    }

    static int nextInt() throws IOException {
        return Integer.parseInt( next() );
    }
    
    static double nextDouble() throws IOException {
        return Double.parseDouble( next() );
    }
    
    static long nextLong() throws IOException {
        return Long.parseLong( next() );
    }
}