#include<bits/stdc++.h>

#define INF 0x3f3f3f3f

using namespace std;

typedef pair<short,int> P;

vector<P> graph1[],graph2[];

int N,M,X,dis1[],dis2[];

bool vis1[],vis2[];

queue<short> q;

int main()

{

    ios::sync_with_stdio();cin.tie();

    int i,j,d,cnt,len,ans=;

    short a,b,id;

    cin>>N>>M>>X;

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

    {

        cin>>a>>b>>d;

        graph1[a].push_back(P(b,d));

        graph2[b].push_back(P(a,d));

    }

    memset(dis1,INF,sizeof dis1);

    memset(dis2,INF,sizeof dis2);

    memset(vis1,false,sizeof vis1);

    memset(vis2,false,sizeof vis2);

    dis1[X]=dis2[X]=;

    vis1[X]=vis2[X]=true;

    q.push(X);

    while(!q.empty())

    {

        id=q.front();

        q.pop();

        cnt=graph1[id].size();

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

        {

            len=dis1[id]+graph1[id][i].second;

            if(!vis1[graph1[id][i].first]||len<dis1[graph1[id][i].first])

            {

                dis1[graph1[id][i].first]=len;

                vis1[graph1[id][i].first]=true;

                q.push(graph1[id][i].first);

            }

        }

    }

    q.push(X);

    while(!q.empty())

    {

        id=q.front();

        q.pop();

        cnt=graph2[id].size();

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

        {

            len=dis2[id]+graph2[id][i].second;

            if(!vis2[graph2[id][i].first]||len<dis2[graph2[id][i].first])

            {

                dis2[graph2[id][i].first]=len;

                vis2[graph2[id][i].first]=true;

                q.push(graph2[id][i].first);

            }

        }

    }

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

    {

        if(i==X)

            continue;

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

    }

    cout<<ans;

    return ;

}