C++ :

#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;

queue<int> q;
int rotb1[1001][1001],rotr1[1001][1001];
int rotb2[1001][1001],rotr2[1001][1001];
long long mi1[1002],mi2[1002];
bool d1[1001],d2[1001];

int main()
{
	//freopen("party.in","r",stdin);
	//freopen("party.out","w",stdout);
	int n,m,k,a,b,r;
	long long maxx=0;
	scanf("%d%d%d",&n,&m,&k);
	for (int i=1;i<=m;i++)
	{
		scanf("%d%d%d",&b,&a,&r);
		rotb1[a][++rotb1[a][0]]=b;
		rotr1[a][++rotr1[a][0]]=r;
		rotb2[b][++rotb2[b][0]]=a;
		rotr2[b][++rotr2[b][0]]=r;
	}
	
	memset(mi1,127,sizeof(mi1));
	memset(mi2,127,sizeof(mi2));
	mi1[k]=mi2[k]=0;
	
	q.push(k);
	while (!q.empty())
	{
		int num=q.front();
		q.pop();
		d1[num]=false;
		for (int i=1;i<=rotb1[num][0];i++)
		{
			b=rotb1[num][i];
			r=rotr1[num][i];
			if (mi1[b]>mi1[num]+r)
			{
				mi1[b]=mi1[num]+r;
				if(!d1[b])
				{
					q.push(b);
					d1[b]=true;
				}
			}
		}
	}
	
	q.push(k);
	while (!q.empty())
	{
		int num=q.front();
		q.pop();
		d2[num]=false;
		for (int i=1;i<=rotb2[num][0];i++)
		{
			b=rotb2[num][i];
			r=rotr2[num][i];
			if (mi2[b]>mi2[num]+r)
			{
				mi2[b]=mi2[num]+r;
				if(!d2[b])
				{
					q.push(b);
					d2[b]=true;
				}
			}
		}
	}
	
	
	for (int i=1;i<=n;i++)
		if(maxx<mi1[i]+mi2[i]&&mi1[i]!=mi1[1001]&&mi2[i]!=mi2[1001])
			maxx=mi1[i]+mi2[i];
	
	printf("%lld",maxx);
	return 0;
	
}