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 Python (3.4.3) (judge verdict: Accepted)

N = int(input())

e_list = [[] for i in range(N)]
for i in range(N-1):
    a,b,c = list(map(int,input().split()))
    a=a-1
    b=b-1
    e_list[a].append([b,c])
    e_list[b].append([a,c])

Q,K = list(map(int,input().split()))
q = []
for i in range(Q):
    x,y=list(map(int,input().split()))
    x=x-1
    y=y-1
    q.append([x,y])

vi = K-1 #時と場合によってここを変える
from collections import deque
Q = deque([vi])
checked_list = [False for i in range(N)]
checked_list[vi]=True
min_path_list = [10**27 for i in range(N)] #問題によりここを変える
min_path_list[vi] = 0
while len(Q)>0:
    v = Q.pop()
    for e in e_list[v]:
        v1,c=e
        if not checked_list[v1]:
            checked_list[v1]=True
            Q.append(v1)
            min_path_list[v1]=min(min_path_list[v1],min_path_list[v]+c) #問題によりここを変える

for a in q:
    x,y=a
    print(min_path_list[x]+min_path_list[y])