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.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;

import java.util.*;

public class A_GENERAL {
   
	// for fast output printing  : use printwriter or stringbuilder
	// remember to close pw using pw.close()
	static StringBuilder sb = new StringBuilder();
	static long seive_size = (long) 1e6;
	static String alpha = "abcdefghijklmnopqrstuvwxyz";
    static ArrayList<Integer> primes = new ArrayList<>();
    static boolean[] set = new boolean[(int) seive_size+1];
    static int n, m;
    static ArrayList<Integer>[] adj;
    static boolean[] visited;
    static ArrayDeque<Integer> q = new ArrayDeque<>();
    static final long MOD = 998244353;
    static long[][] arr;
    
    
    
	public static void main(String[] args) {
		PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
		MyScanner sc = new MyScanner();
		n = sc.nextInt();
		init(n);
		for(int i = 1; i <= n-1; i++) {
			int u = sc.nextInt();
			int v = sc.nextInt();
			adj[u].add(v);
			adj[v].add(u);
		}
		double tot = dfs(1, 0);
		out.println(tot);
		out.close();
	}

	public static double dfs(int u, int d) {
		visited[u] = true;
		double res = 0;
		int childs = 0;
		for(int v : adj[u]) {
			if(!visited[v]) {
				childs++;
				res += dfs(v, d+1);
			}
		}
		return (childs == 0) ? d : res*(1.0/childs);
	}
	
	public static class Pair {
		long f;
		long s;
		Pair(long f, long s) {
			this.f = f;
			this.s = s;
		}
	}
	public static void init(int n) {
    	adj = new ArrayList[n+1];
    	visited = new boolean[n+1];
    	for(int i = 1; i <= n; i++)
			adj[i] = new ArrayList();
    }
	// print string "s" multiple times 
	// prefer to use this function for multiple printing
	public static String mp(String s, int times) {
		return String.valueOf(new char[times]).replace("\0", s);
	}
	// take log with base 2
 	public static long log2(long k) {
 		return 63-Long.numberOfLeadingZeros(k);
 	}

 	// using lambda function for sorting
   	public static void lambdaSort() {
   		Arrays.sort(arr, (a, b) -> Double.compare(a[0], b[0]));
   	}
  	
  	// (n choose k) = (n/k) * ((n-1) choose (k-1))
  	public static long choose(long n, long k) {
 		return (k == 0) ? 1 : (n*choose(n-1, k-1))/k;
 	}

 	// just for keeping gcd function for other personal purposes
 	public static long gcd(long a, long b) {
 		return (a == 0) ? b : gcd(b%a, a);
 	}
 	
	public static long max(long... as) {
        long max = Long.MIN_VALUE;
        for (long a : as) max = Math.max(a, max);
        return max;
    }

    public static long min(int... as) {
        long min = Long.MAX_VALUE;
        for (long a : as) min = Math.min(a, min);
        return min;
    }
 	
    public static long modpow(long x, long n, long mod) {
    	if(n == 0) return 1%mod;
    	long u = modpow(x, n/2, mod);
    	u = (u*u)%mod;
    	if(n%2 == 1) u = (u*x)%mod;
    	return u;
    }
 	// ======================= binary search (lower and upper bound) =======================
	public static int lowerBound(long[] a, int x) {
		int lo = 0;
 		int hi = a.length-1;
 		int ans = -1;
 		while(lo <= hi) {
 			int mid = (lo+hi)/2;
 			if(x < a[mid]) {
 				hi = mid-1;
 			} else if(x > a[mid]) {
 				lo = mid+1;
 			} else if(lo != hi) {
 				 hi = mid-1; 		// for first occurrence
 				 ans = mid;
 			} else {
 				return mid;
 			}
 		}
 		return ans;
	}
	
	public static int upperBound(long[] a, long x) {
		int lo = 0;
		int hi = a.length-1;
		int ans = -1;
		while(lo <= hi) {
			int mid = (lo+hi)/2;
			if(x < a[mid]) {
				hi = mid-1;
			} else if(x > a[mid]) {
				lo = mid+1;
			} else if(lo != hi) {
				lo = mid+1;			// for last occurrence
				ans = mid;
			} else {
				return mid;
			}
		}
		return ans;
	}
	// ================================================================

	// ================== SEIVE OF ERATOSTHENES =======================
	// Complexity : O(N * log(log(N)))       ( almost O(N) )
	public static void generatePrimes() {
		// set.add(0);
		// set.add(1);
		Arrays.fill(set, true);
		set[0] = false;
		set[1] = false;
		for(int i = 2; i <= seive_size; i++) {
			if(set[i]) {
				for(long j = (long) i*i; j <= seive_size; j+=i) 
					set[(int)j] = false;
				primes.add(i);
			}
		}
	}
  
	public static boolean isPrime(long N) {
		if(N <= seive_size) return set[(int)N];
		for (int i = 0; i < (int)primes.size(); i++)
			if (N % primes.get(i) == 0) return false;
		return true;
	}
	// ===========================================================
  
 	// ================ Permutation of String ====================
 	public static void permute(String str) {
 		permute(str, 0, str.length()-1);
 	}
 	public static void permute(String str, int l, int r) 
    { 
        if (l == r) 
            System.out.println(str); 
        else
        { 
            for (int i = l; i <= r; i++) 
            { 
                str = swap(str,l,i); 
                permute(str, l+1, r); 
                str = swap(str,l,i); 
            } 
        } 
    }
	public static String swap(String a, int i, int j) 
    { 
        char temp; 
        char[] charArray = a.toCharArray(); 
        temp = charArray[i] ; 
        charArray[i] = charArray[j]; 
        charArray[j] = temp; 
        return String.valueOf(charArray); 
    } 
	// Union-find
	void makeSet(int parent[], int rank[]) {

		int i;
		for(i = 0; i < parent.length; i++) {
			parent[i] = i;
			rank[i] = 0;
		}
	}
	public static int find(int u, int parent[]) {

		if(parent[u] == u)	return u;

		int v = find(parent[u], parent);
		parent[u] = v;
		return v;

	}
	public static boolean connected(int u, int v, int[] parent) {
		return find(u, parent) == find(v, parent);
	}
	public static void Union(int u, int v, int rank[], int parent[]) {

		int x = find(u, parent);				//root of u
		int y = find(v, parent);				//root of v

		if(x == y)		return;
		if(rank[x] == rank[y]) {
			parent[y] = x;
			rank[x]++;
		}
		else if(rank[x] > rank[y]) {
			parent[y] = x;
		}
		else {
			parent[x] = y;
		}

	}
	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;
		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}
		String next() {while (st == null || !st.hasMoreElements()) {
			try {st = new StringTokenizer(br.readLine());}
			catch (IOException e) {e.printStackTrace();}}
		return st.nextToken();}
		int nextInt() {return Integer.parseInt(next());}
		long nextLong() {return Long.parseLong(next());}
		double nextDouble() {return Double.parseDouble(next());}
		String nextLine(){String str = "";
		try {str = br.readLine();}
		catch (IOException e) {e.printStackTrace();}
		return str;}
		int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
	}

}