#include <cstdio>

 #include <iostream>

 #include <algorithm>

 #include <queue>

 #include <cstring>

 using namespace std;

 const int maxn = ;

 const int inf = 0x7fffffff;

 int n, m, x, dis1[maxn], dis2[maxn];

 bool vis1[maxn] = {}, vis2[maxn] = {};

 struct edge{

     int len, to, next;

 }e1[maxn], e2[maxn];

 int head1[maxn], head2[maxn], cnt1, cnt2;

 void SPFA1()

 {

     queue<int> q1;

     vis1[x] = ;

     dis1[x] = ;

     q1.push(x);

     while(!q1.empty())

     {

         int now1 = q1.front();

         q1.pop();

         vis1[now1] = ;

         for(int i = head1[now1]; i!= ; i = e1[i].next)

         {

             if(dis1[e1[i].to] > dis1[now1]+e1[i].len)

             {

                 dis1[e1[i].to] = dis1[now1]+e1[i].len;

                 if(!vis1[e1[i].to])

                 {

                     vis1[e1[i].to] = ;

                     q1.push(e1[i].to);

                 }

             }

         }

     }

 }

 void SPFA2()

 {

     queue<int> q2;

     vis2[x] = ;

     dis2[x] = ;

     q2.push(x);

     while(!q2.empty())

     {

         int now2 = q2.front();

         q2.pop();

         vis2[now2] = ;

         for(int i = head2[now2]; i ; i = e2[i].next)

         {

             if(dis2[e2[i].to] > dis2[now2]+e2[i].len)

             {

                 dis2[e2[i].to] = dis2[now2]+e2[i].len;

                 if(!vis2[e2[i].to])

                 {

                     vis2[e2[i].to] = ;

                     q2.push(e2[i].to);

                 }

             }

         }

     }

 }

 int main()

 {

     cin>>n>>m>>x;

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

     {

         dis2[i] = inf;

         dis1[i] = inf;

     }

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

     {

         int u,v,w;

         cin>>u>>v>>w;

         e1[i].to = v;

         e1[i].len = w;

         e1[i].next = head1[u];

         head1[u] = i;

         e2[i].to = u;

         e2[i].len = w;

         e2[i].next = head2[v];

         head2[v] = i;

     }

     SPFA1();

     SPFA2();

     int ans = ;

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

     {

         ans = max(dis1[i]+dis2[i],ans);

     }

     cout<<ans;

     return ;

 }