//

 //  main.cpp

 //  sicily-1024

 //

 //  Created by ashley on 14-10-13.

 //  Copyright (c) 2014年 ashley. All rights reserved.

 //

 #include <iostream>

 #include <vector>

 using namespace std;

 typedef struct

 {

     int left;

     int right;

     int weight;

 }edge;

 vector<edge> route;

 vector<edge> adj[];

 bool isVisited[];

 void breadthSearch(int source, int &length, int pathLength)

 {

     isVisited[source] = true;

     for (int i = ; i < (int)adj[source].size(); i++) {

         if (isVisited[adj[source][i].right] == false || isVisited[adj[source][i].left] == false) {

             if (pathLength + adj[source][i].weight > length) {

                 length = pathLength + adj[source][i].weight;

             }

             if (isVisited[adj[source][i].right] == false) {

                 breadthSearch(adj[source][i].right, length, pathLength + adj[source][i].weight);

             }

             if (isVisited[adj[source][i].left] == false) {

                 breadthSearch(adj[source][i].left, length, pathLength + adj[source][i].weight);

             }

         }

     }

 }

 int main(int argc, const char * argv[])

 {

     int nodeNum, capital;

     while (cin >> nodeNum >> capital) {

         for (int i = ; i < ; i++) {

             adj[i].clear();

             isVisited[i] = false;

         }

         //memset(adj, 0, sizeof(adj));

         //memset(isVisited, 0, sizeof(isVisited));

         int l, r, w;

         for (int i = ; i < nodeNum - ; i++) {

             cin >> l >> r >> w;

             adj[l].push_back(edge{l, r, w});

             adj[r].push_back(edge{l, r, w});

         }

         int longest = ;

         breadthSearch(capital, longest, );

         cout << longest << endl;

     }

     return ;

 }