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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> P;
typedef long long ll;
typedef long double ld;
const int inf=1e9+7;
const ll longinf=1LL<<60;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
#define F first
#define S second

const int mx=100010;
const ll mod=1e9+7;

typedef vector<vector<pair<ll,int>>> wgraph;
typedef pair<ll,int> pli;

vector<ll> bfs(wgraph v,int x){
  priority_queue<pli,vector<pli>,greater<pli>> q;
  vector<ll> dist(v.size(),longinf);
  dist[x]=0;
  q.push({0LL,x});
  
  while(q.size()){
    pli p=q.top(); q.pop();
    ll d=p.F, now=p.S;
    if(dist[now]<d){ continue; }
    for(auto to:v[now]){
      if(dist[to.S]>d+to.F){
        dist[to.S] = d+to.F;
        q.push({dist[to.S], to.S});
      }
    }
  }
  return dist;
}

int main(){
  int n;
  cin >> n;
  wgraph v(n);
  rep(i,n-1){
    int x,y,c;
    cin >> x >> y >> c; x--; y--;
    v[x].push_back({c,y});
    v[y].push_back({c,x});
  }
  int q,k; cin >> q >> k; k--;
  vector<ll> data=bfs(v,k);
  rep(i,q){
    int x,y;
    cin >> x >> y; x--; y--;
    cout << data[x]+data[y] << endl;
  }
  return 0;
}