D

//两次dijkstra
#include <iostream>
#include <algorithm>

#define Faster ios::sync_with_stdio(false),cin.tie(0)
#define Read freopen("in.txt","r",stdin),freopen("out.txt","w",stdout)
#define Close fclose(stdin),fclose(stdout)
const int INF = 0xffffff;
const int maxn = 1005;
using namespace std;

int mp[maxn][maxn];
bool v[maxn];
bool v2[maxn];
int dis[maxn];
int dis2[maxn];

int n;

void dijkstra(int x){
    for(int i = 1;i <= n;i++){
        dis[i] = mp[x][i];
        dis2[i] = mp[i][x];
        v[i] = true;
        v2[i] = true;
    }
    dis[x] = dis2[x] = 0;
    v[x] = v2[x] = false;

    for(int i = 1;i < n;i++){
        int Min = INF;
        int p;
        for(int j = 1;j <= n;j++){
            if(v[j] && dis[j] < Min){
                Min = dis[j];
                p = j;
            }
        }
        if(Min == INF)
            break;
        v[p] = false;
        for(int j = 1;j <= n;j++){
            if(v[j] && dis[j] > dis[p] + mp[p][j])
                dis[j] = dis[p] + mp[p][j];
        }
    }

    for(int i = 0;i < n;i++){
        int Min = INF;
        int p;
        for(int j = 1;j <= n;j++){
            if(v2[j] && dis2[j] < Min){
                Min = dis2[j] ;
                p = j;
            }
        }
        if(Min == INF)
            break;
        v2[p] = false;
        for(int j = 1;j <= n;j++){
            if(v2[j] && dis2[j] > dis2[p] + mp[j][p])
                dis2[j] = dis2[p] + mp[j][p];
        }
    }
}

int main(){
    Faster;
    int m, k;
    cin >> n >> m >> k;
    for(int i = 0;i <= n;i++)
    for(int j = 0;j <= n;j++){
        mp[i][j] = INF;
        if(i == j)
            mp[i][j] = 0;
    }
    for(int i = 0;i < m;i++){
        int x, y, z;
        cin >> x >> y >> z;
        if(mp[x][y] > z)
            mp[x][y] = z;
    }

    dijkstra(k);

    int ans = 0;
    for(int i = 1;i <= n;i++){
        ans = max(ans, dis[i]+dis2[i]);
        //cout << "go: " << dis2[i] << " , ovel : " << dis[i] << endl;
    }
    cout << ans << endl;
    return 0;
}