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.util.*;

import java.io.*;

public class A {
	static BufferedReader br;
	static PrintWriter pw;
	static int inf = (int) 1e9;
	static long mod = (long) 1e9 + 7;

	static ArrayList<Integer>[] graph;
	static int n;

	public static void main(String[] args) throws NumberFormatException, IOException, InterruptedException {
//		br = new BufferedReader(new FileReader(new File("chief.in")));
//		br = new BufferedReader(new InputStreamReader(System.in));
		Scanner sc = new Scanner(System.in);
		pw = new PrintWriter(System.out);
		n = sc.nextInt();
		graph = new ArrayList[n];
		for (int i = 0; i < graph.length; i++) {
			graph[i] = new ArrayList<>();
		}
		for (int i = 0; i < n - 1; i++) {
			int u = sc.nextInt() - 1;
			int v = sc.nextInt() - 1;
			graph[u].add(v);
			graph[v].add(u);
		}

		pw.println(dfs(0, -1, 0));
		pw.flush();
		pw.close();

	}

	static long[][] dp;
	static int[] color, down, total;

	static double dfs(int u, int pa, int l) {
		double sum = 0;
		double prop = (1.0 / (graph[u].size()-1));
		if (pa == -1)
			prop = (1.0 / graph[u].size());
		for (int v : graph[u]) {
			if (v == pa)
				continue;
			sum += (prop) * dfs(v, u, l + 1);
		}
		if (sum == 0)
			return l;
		return sum;
	}
//
//	static void dfs2(int u, int pa, int costOFEdge) {
//		if (pa == -1)
//			total[u] = down[u];
//		else
//			total[u] = costOFEdge == 0 ? total[pa] + 1 : total[pa] - 1;
//
//		for (pair v : graph[u]) {
//			if (v.x == pa)
//				continue;
//			dfs2(v.x, u, v.y);
//		}
//	}

//	static long[] f, g;
//
//	static void numOfSubtrees(int u, int pa) {
//		f[u] = 1;
//		for (int v : graph[u]) {
//			if (v == pa)
//				continue;
//			numOfSubtrees(v, u);
//			f[u] *= (1 + f[v]);
//			g[u] += f[v] + g[v];
//		}
//	}

	static ArrayList<Integer> primes; // generated by sieve

	/*
	 * 1. Generating a list of prime factors of N
	 */
	static ArrayList<Long> primeFactors(Long N) // O(sqrt(N) / ln sqrt(N))
	{
		ArrayList<Long> factors = new ArrayList<Long>(); // take abs(N) in case of -ve integers
		int idx = 0, p = primes.get(idx);

		while (p * p <= N) {
			if (N % p == 0)
				factors.add((long) p);
			while (N % p == 0) {
				N /= p;
			}
			if (idx + 1 == primes.size())
				break;
			p = primes.get(++idx);
		}

		if (N != 1) // last prime factor may be > sqrt(N)
			factors.add(N); // for integers whose largest prime factor has a power of 1
		return factors;
	}

	static int[] isComposite;

	static void sieve(int N) // O(N log log N)
	{
		isComposite = new int[N + 1];
		isComposite[0] = isComposite[1] = 1; // 0 indicates a prime number
		primes = new ArrayList<Integer>();

		for (int i = 2; i <= N; ++i) // can loop till i*i <= N if primes array is not needed O(N log log sqrt(N))
			if (isComposite[i] == 0) // can loop in 2 and odd integers for slightly better performance
			{
				primes.add(i);
				if (1l * i * i <= N)
					for (int j = i * i; j <= N; j += i) // j = i * 2 will not affect performance too much, may alter in
														// modified sieve
						isComposite[j] = 1;
			}
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

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

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

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public boolean ready() throws IOException {
			return br.ready();
		}

	}

	static int m, k;

	static double[] memo;
	static ArrayList<Integer>[] adj;

	static long gcd(long a, long b) {
		if (a == 0)
			return b;
		return gcd(b % a, a);
	}

	// method to return LCM of two numbers
	static long lcm(long a, long b) {
		return (a * b) / gcd(a, b);
	}

	static double dis(int x, int y, int z, int w) {
		return Math.sqrt((x - z) * (x - z) + (y - w) * (y - w));
	}

	static int[] nxtarr() throws IOException {
		StringTokenizer st = new StringTokenizer(br.readLine());
		int[] a = new int[st.countTokens()];
		for (int i = 0; i < a.length; i++) {
			a[i] = Integer.parseInt(st.nextToken());
		}
		return a;
	}

	static long[] nxtarrLong() throws IOException {
		StringTokenizer st = new StringTokenizer(br.readLine());
		long[] a = new long[st.countTokens()];
		for (int i = 0; i < a.length; i++) {
			a[i] = Long.parseLong(st.nextToken());
		}
		return a;
	}

	static class pair implements Comparable<pair> {
		int x;
		int y;

		public pair(int d, int u) {
			x = d;
			y = u;
		}

		@Override
		public int compareTo(pair o) {
			// TODO Auto-generated method stub
			if (y == o.y)
				return x - o.x;
			return y - o.y;
		}

	}

	static class triple implements Comparable<triple> {
		int x;
		int y;
		int z;

		public triple(int a, int b, int c) {
			x = a;
			y = b;
			z = c;
		}

		@Override
		public int compareTo(triple o) {
			// TODO Auto-generated method stub
			return x - o.x;
		}
	}

}