//It is made by HolseLee on 17th Aug 2018
//华山论剑
#include<bits/stdc++.h>
#define Max(a,b) (a)>(b)?(a):(b)
using namespace std;

const int N=1001;
const int M=1e5+7;
int n,m,tag,h1[N],h2[N],cnt1,cnt2,dis1[N],dis2[N],ans;
bool vis[N];
struct Node{
    int to,val,nxt;
}e1[M],e2[M];
queue<int>t;

inline int read()
{
    char ch=getchar();int num=0;bool flag=false;
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)flag=true;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){num=num*10+ch-‘0‘;ch=getchar();}
    return flag?-num:num;
}

inline void add1(int x,int y,int z)
{
    e1[++cnt1].to=y;
    e1[cnt1].val=z;
    e1[cnt1].nxt=h1[x];
    h1[x]=cnt1;
}

inline void add2(int x,int y,int z)
{
    e2[++cnt2].to=y;
    e2[cnt2].val=z;
    e2[cnt2].nxt=h2[x];
    h2[x]=cnt2;
}

void spfa1()
{
    memset(vis,0,sizeof(vis));
    memset(dis1,0x7f,sizeof(dis1));
    while(!t.empty())t.pop();
    dis1[tag]=0;vis[tag]=1;
    t.push(tag);
    int x,y;
    while(!t.empty()){
        x=t.front();t.pop();
        vis[x]=0;
        for(int i=h1[x];i!=-1;i=e1[i].nxt){
            y=e1[i].to;
            if(dis1[y]>dis1[x]+e1[i].val){
                dis1[y]=dis1[x]+e1[i].val;
                if(!vis[y])t.push(y),vis[y]=1;
            }
        }
    }
}

void spfa2()
{
    memset(vis,0,sizeof(vis));
    memset(dis2,0x7f,sizeof(dis2));
    while(!t.empty())t.pop();
    dis2[tag]=0;vis[tag]=1;
    t.push(tag);
    int x,y;
    while(!t.empty()){
        x=t.front();t.pop();
        vis[x]=0;
        for(int i=h2[x];i!=-1;i=e2[i].nxt){
            y=e2[i].to;
            if(dis2[y]>dis2[x]+e2[i].val){
                dis2[y]=dis2[x]+e2[i].val;
                if(!vis[y])t.push(y),vis[y]=1;
            }
        }
    }
}

int main()
{
    n=read();m=read();tag=read();
    memset(h1,-1,sizeof(h1));
    memset(h2,-1,sizeof(h2));
    int x,y,z;
    for(int i=1;i<=m;++i){
        x=read();y=read();z=read();
        add1(x,y,z);add2(y,x,z);
    }
    spfa1();spfa2();
    for(int i=1;i<=n;++i){
        ans=Max(ans,dis1[i]+dis2[i]);
    }
    printf("%d\n",ans);
    return 0;
}