#include<cstdio>        //固定起点，求出到其它顶点的最长路径，邻接表+优先队列实现Dijkstra算法
#include<cstring>
#include<queue>
#include <algorithm>
using namespace std;

const int INF = -1<<30;
const int MAXN = 10000;    
const int MAXM = 20000;    

int n, m;    //结点数和边数，结点下标从0开始
int first[MAXN], distD[MAXN],done[MAXN];
int u[MAXM], v[MAXM], w[MAXM], Next[MAXM];    //first[u]保存结点u的第一条边的编号，next[e]表示编号为e的边的“下一条边”的编号

typedef pair<int,int> pii;
void init()
{
    fill(first,first+n,-1);
    m=0;
    for(int k=0;k<n-1;++k)    //根据题意的“连通性”和“恰好包含n-1条边”,必不含圈
    {
        scanf("%d%d%d", &u[m], &v[m], &w[m]);
        u[m]--;v[m]--;
        Next[m] = first[u[m]];
        first[u[m]] = m;
        m++;
        u[m]=v[m-1];    //无向边
        v[m]=u[m-1];
        w[m]=w[m-1];
        Next[m] = first[u[m]];
        first[u[m]] = m;
        m++;
    }
}
void Dijkstra(int st)
{
    priority_queue<pii, vector<pii>, less<pii> > q;        //最长路径,所以是 less<pii>
    fill(distD,distD+n,INF);    //注意这里的INF应该是负无穷
    distD[st]=0;
    fill(done,done+n,0);
    q.push(make_pair(distD[st], st));
    int cnt=0;
    while(!q.empty()) 
    {
        pii u = q.top();
        q.pop();
        int x = u.second;
        if(done[x])
            continue;
        done[x] = 1;
        if(++cnt==n)    //n个结点
        {
            break;
        }
        for(int e = first[x]; e != -1; e = Next[e]) 
            if(!done[v[e]]&&distD[v[e]] < distD[x]+w[e]) 
            {
                distD[v[e]] = distD[x] + w[e];
                q.push(make_pair(distD[v[e]], v[e]));
            }
    }
}
int main() 
{
    int k;
    while(scanf("%d%d",&n,&k)==2)
    {
        init();
        Dijkstra(k-1);
        printf("%d\n",*max_element(distD,distD+n));
    }
    return 0;
}