#include<stdio.h>

#include<stdlib.h>

#include<math.h>

#include<string.h>

#define max(a, b)(a > b ? a : b)

#define min(a, b)(a < b ? a : b)

#define INF 0xffffff

#define N 1010

int G1[N][N], G2[N][N];

bool vis[N];

int dist1[N], dist2[N], n;

void Init()

{

    int i, j;

    memset(vis, false, sizeof(vis));

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

    {

        dist1[i] = INF;

        dist2[i] = INF;

        for(j =  ; j <= n ; j++)

           {

               G1[i][j] = INF;

               G2[i][j] = INF;

           }

    }

}

void Dij(int G[][N], int dist[], int x)

{

    int index, Min, i, j;

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

        dist[i] = INF;

    dist[x] = ;

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

    {

        index = ;

        Min = INF;

        for(j =  ; j <= n ; j++)

        {

            if(!vis[j] && dist[j] < Min)

            {

                Min = dist[j];

                index = j;

            }

        }

        vis[index] = true;

        for(j =  ; j <= n ; j++)

        {

            if(!vis[j] && dist[j] > dist[index] + G[index][j])

                dist[j] = dist[index] + G[index][j];

        }

    }

}

int main()

{

    int m, x, i, a, b, t, Max;

    while(scanf("%d%d%d", &n, &m, &x) != EOF)

    {

        Init();

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

        {

            scanf("%d%d%d", &a, &b, &t);

            G1[a][b] = t;

            G2[b][a] = t;

        }

       Dij(G1, dist1, x);

       memset(vis, false, sizeof(vis));

       Dij(G2, dist2, x);

       Max = ;

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

           Max = max(Max, dist1[i] + dist2[i]);

        printf("%d\n", Max);

    }

    return ;

}