Problem:
Score : 400 points

Problem Statement

You are given a tree with N vertices.

Here, a tree is a kind of graph, and more specifically, a connected undirected graph with N-1 edges, where N is the number of its vertices.

The i-th edge (1≤i≤N-1) connects Vertices a_i and b_i, and has a length of c_i.

You are also given Q queries and an integer K. In the j-th query (1≤j≤Q):

find the length of the shortest path from Vertex x_j and Vertex y_j via Vertex K.

Constraints

3≤N≤10^5

1≤a_i,b_i≤N (1≤i≤N-1)

1≤c_i≤10^9 (1≤i≤N-1)

The given graph is a tree.

1≤Q≤10^5

1≤K≤N

1≤x_j,y_j≤N (1≤j≤Q)

x_j≠y_j (1≤j≤Q)

x_j≠K,y_j≠K (1≤j≤Q)

Input

Input is given from Standard Input in the following format:

N
a_1 b_1 c_1
:
a_{N-1} b_{N-1} c_{N-1}
Q K
x_1 y_1
:
x_{Q} y_{Q}

Output

Print the responses to the queries in Q lines.

In the j-th line j(1≤j≤Q), print the response to the j-th query.

Sample Input 1

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

Sample Output 1

3
2
4

The shortest paths for the three queries are as follows:

Query 1: Vertex 2 → Vertex 1 → Vertex 2 → Vertex 4 : Length 1+1+1=3

Query 2: Vertex 2 → Vertex 1 → Vertex 3 : Length 1+1=2

Query 3: Vertex 4 → Vertex 2 → Vertex 1 → Vertex 3 → Vertex 5 : Length 1+1+1+1=4

Sample Input 2

7
1 2 1
1 3 3
1 4 5
1 5 7
1 6 9
1 7 11
3 2
1 3
4 5
6 7

Sample Output 2

5
14
22

The path for each query must pass Vertex K=2.

Sample Input 3

10
1 2 1000000000
2 3 1000000000
3 4 1000000000
4 5 1000000000
5 6 1000000000
6 7 1000000000
7 8 1000000000
8 9 1000000000
9 10 1000000000
1 1
9 10

Sample Output 3

17000000000

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

class Edge{
	int to;
	int cost;
	public Edge(int to, int cost) {
		this.to = to;
		this.cost = cost;
	}
}

public class Main {
	static List<Edge>[] tree;
	static long result = 0;

	static void dfs(boolean[] seen, int parent, int goal, long cost_from_p) {
		seen[parent] = true;
		for(Edge next : tree[parent]) {
			if(seen[next.to]) continue;
			long costs = cost_from_p + next.cost;
			if(next.to == goal) result += costs;
			dfs(seen, next.to, goal, costs);
		}
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		boolean[] seen = new boolean[n];
		tree = new ArrayList[n];

		for(int i = 0; i < n; i++) {
			tree[i] = new ArrayList<>();
		}

		for(int i = 0; i < n - 1; i++) {
			int a = sc.nextInt() - 1;
			int b = sc.nextInt() - 1;
			int c = sc.nextInt();
			tree[a].add(new Edge(b, c));
			tree[b].add(new Edge(a, c));
		}

		int q = sc.nextInt();
		int k = sc.nextInt() - 1;
		int[] x = new int[q];
		int[] y = new int[q];

		for(int i = 0; i < q; i++) {
			x[i] = sc.nextInt() - 1;
			y[i] = sc.nextInt() - 1;
		}

		for(int i = 0; i < q; i++) {
			dfs(seen, x[i], k, 0);
			Arrays.fill(seen, false);
			dfs(seen, k, y[i], 0);
			Arrays.fill(seen, false);
			System.out.println(result);
			result = 0;
		}
		sc.close();
	}
}