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

using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Convert;
using static System.Math;
using Pair = System.Tuple<int, int>;
using Edge = System.Tuple<int, int, long>;
//using Debug;
//using static System.Globalization.CultureInfo;

class Program
{
    static void Main(string[] args)
    {
        Solve();
        //WriteLine(Solve());
    }
    static void Solve()
    {
        var num = Input.num;
        var ps = P.Make(num, num - 1);
        var qk = Input.ar;
        ps[qk[1] - 1].Weight = 0;
        var que = new Queue<P>();
        que.Enqueue(ps[qk[1]-1]);
        while (que.Count != 0)
        {
            var p = que.Dequeue();
            foreach (var ad in p.adj)
            {
                if (ps[ad].Weight != Input.Inf || ad == qk[1] - 1) continue;
                ps[ad].Weight = p.Weight + p.dist[ad];
                que.Enqueue(ps[ad]);
            }
        }
        var res = new long[qk[0]];
        for(var i = 0; i < qk[0]; i++)
        {
            var xy = Input.ar;
            res[i] = ps[xy[0] - 1].Weight + ps[xy[1] - 1].Weight;
        }
        WriteLine(string.Join("\n", res));
    }
}

public class Input
{
    public static string read => ReadLine();
    public  static int[] ar => Array.ConvertAll(read.Split(' '), int.Parse);
    public  static int num => ToInt32(read);
    public static long[] arL => Array.ConvertAll(read.Split(' '), long.Parse);
    public  static long numL => ToInt64(read);
    public static char[][] gred(int h) 
        => Enumerable.Repeat(0, h).Select(v => read.ToCharArray()).ToArray();
    public static int[][] ar2D(int num)
        => Enumerable.Repeat(0, num).Select(v => ar).ToArray();
    public static long[][] arL2D(int num)
        => Enumerable.Repeat(0, num).Select(v => arL).ToArray();
    public const long Inf = (long)1e18;
    public const double eps = 1e-6;
    public  const string Alfa = "abcdefghijklmnopqrstuvwxyz";
    public  const int MOD = 1000000007;
}

public class P : IComparable<P>
{
    public int index;
    public List<int> adj;
    public List<int> rev;
    public Dictionary<int, int> dist;
    public int parent;
    public long Weight { get; set; }
    public P(int index,long Weight=Input.Inf)
    {
        this.index = index;
        adj = new List<int>();
        rev = new List<int>();
        dist = new Dictionary<int, int>();
        this.Weight = Weight;
    }
    public static P[] Make(int num, int edge = 0, bool isNotDirected = true, bool isWeighted = true)
    {
        var ps = Enumerable.Range(0, num).Select(v => new P(v)).ToArray();
        for (var i = 0; i < edge; i++)
        {
            var inp = Input.ar;
            inp[0]--;
            inp[1]--;
            for (var j = 0; j <= ToInt32(isNotDirected); j++)
            {
                ps[inp[j]].adj.Add(inp[1 - j]);
                if (!isNotDirected)
                    ps[inp[1 - j]].rev.Add(inp[j]);
                if (isWeighted)
                    ps[inp[j]].dist[inp[1 - j]] = inp[2];
            }
        }
        return ps;
    }
    public override string ToString()
        => $"{index + 1} {Weight}";
    public override int GetHashCode()
        => index.GetHashCode();
    public int CompareTo(P p)
        => Weight.CompareTo(p.Weight);
}