Problem:
Score : 600 points

Problem Statement

We have a tree with N vertices numbered 1 to N.
The i-th edge in this tree connects Vertex a_i and Vertex b_i.

Consider painting each of these edges white or black. There are 2^{N-1} such ways to paint the edges. Among them, how many satisfy all of the following M restrictions?

The i-th (1 \leq i \leq M) restriction is represented by two integers u_i and v_i, which mean that the path connecting Vertex u_i and Vertex v_i must contain at least one edge painted black.

Constraints

2 \leq N \leq 50

1 \leq a_i,b_i \leq N

The graph given in input is a tree.

1 \leq M \leq \min(20,\frac{N(N-1)}{2})

1 \leq u_i < v_i \leq N

If i \not= j, either u_i \not=u_j or v_i\not=v_j

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 b_1
:
a_{N-1} b_{N-1}
M
u_1 v_1
:
u_M v_M

Output

Print the number of ways to paint the edges that satisfy all of the M conditions.

Sample Input 1

3
1 2
2 3
1
1 3

Sample Output 1

3

The tree in this input is shown below:

All of the M restrictions will be satisfied if Edge 1 and 2 are respectively painted (white, black), (black, white), or (black, black), so the answer is 3.

Sample Input 2

2
1 2
1
1 2

Sample Output 2

1

The tree in this input is shown below:

All of the M restrictions will be satisfied only if Edge 1 is painted black, so the answer is 1.

Sample Input 3

5
1 2
3 2
3 4
5 3
3
1 3
2 4
2 5

Sample Output 3

9

The tree in this input is shown below:

Sample Input 4

8
1 2
2 3
4 3
2 5
6 3
6 7
8 6
5
2 7
3 5
1 6
2 8
7 8

Sample Output 4

62

The tree in this input is shown below:

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
	public class Program
	{
		static List<Edge>[] to_;
		static void Main(string[] args)
		{
			var cin = new Scanner2();
			int n = cin.Int();
			to_ = new List<Edge>[n];
			for (int i = 0; i < n; i++) {
				to_[i] = new List<Edge>();
			}

			for (int i = 0; i < n - 1; i++) {
				int a = cin.Int() - 1;
				int b = cin.Int() - 1;
				to_[a].Add(new Edge(b, i));
				to_[b].Add(new Edge(a, i));
			}

			int m = cin.Int();
			var edgeBits = new long[m];
			for (int i = 0; i < m; i++) {
				int u = cin.Int() - 1;
				int v = cin.Int() - 1;
				var root = new List<long>();
				DFS(u, v, -1, root);

				foreach (int e in root) {
					edgeBits[i] |= (1L << e);
				}
			}

			long ans = 0;
			for (long i = 0; i < 1L << m; i++) {
				long flag = 0;
				for (int j = 0; j < m; j++) {
					if (((1L << j) & i) != 0) {
						flag |= edgeBits[j];
					}
				}

				int whiteCount = PopCount(flag);
				long temp = 1L << (n - 1 - whiteCount);
				if (PopCount(i) % 2 == 0) {
					ans += temp;
				} else {
					ans -= temp;
				}
			}

			Console.WriteLine(ans);
		}

		static bool DFS(int src, int dst, int pre, List<long> root)
		{
			if (src == dst) {
				return true;
			}

			foreach (var next in to_[src]) {
				if (next.To == pre) {
					continue;
				}

				if (DFS(next.To, dst, src, root)) {
					root.Add(next.ID);
					return true;
				}
			}

			return false;
		}

		static int PopCount(long bits)
		{
			int count = 0;
			for (int i = 0; i < 63; i++) {
				if ((bits & 1L << i) != 0) {
					++count;
				}
			}

			return count;

			/*
			bits = (bits & 0x55555555) + (bits >> 1 & 0x55555555);
			bits = (bits & 0x33333333) + (bits >> 2 & 0x33333333);
			bits = (bits & 0x0f0f0f0f) + (bits >> 4 & 0x0f0f0f0f);
			bits = (bits & 0x00ff00ff) + (bits >> 8 & 0x00ff00ff);
			return (int)((bits & 0x0000ffff) + (bits >> 16 & 0x0000ffff));
			*/
		}
	}

	struct Edge
	{
		public int To;
		public int ID;
		public Edge(int to, int id)
		{
			To = to;
			ID = id;
		}
	}

	public class Scanner2
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private string[] buf_;
		private int index_;
		Func<string> reader_;

		public Scanner2(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Int() + add;
			}
			return Array;
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Long() + add;
			}
			return Array;
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Double() + add;
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}