#include<iostream>#include<cstdio>#include<cstring>#include<queue>#include<algorithm>#define maxv 1050#define maxe 200500#define inf 2000000000using namespace std;queue <int> q;int n,m,s,x,y,z,g[maxv],nume=0,dis[maxv][3];struct edge{    int v,w,nxt;}e[maxe];bool vis[maxv];void addedge(int u,int v,int w){    e[++nume].v=v;    e[nume].w=w;    e[nume].nxt=g[u];    g[u]=nume;}void spfa(int type){    for (int i=1;i<=n;i++)    {        dis[i][type]=inf;        vis[i]=false;    }    dis[s][type]=0;vis[s]=true;q.push(s);    while (!q.empty())    {        int head=q.front();q.pop();        for (int i=g[head];i;i=e[i].nxt)        {            int v=e[i].v;             if ((i%2==type) && (dis[v][type]>dis[head][type]+e[i].w))            {                dis[v][type]=dis[head][type]+e[i].w;                if (!vis[v]) {vis[v]=true;q.push(v);}            }        }        vis[head]=false;    }}int main(){    scanf("%d%d%d",&n,&m,&s);    for (int i=1;i<=m;i++)    {        scanf("%d%d%d",&x,&y,&z);        addedge(x,y,z);addedge(y,x,z);    }    spfa(0);    spfa(1);    int ans=0;    for (int i=1;i<=n;i++)        ans=max(ans,dis[i][0]+dis[i][1]);    printf("%d\n",ans);    return 0;}