#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("Sate.txt");
ofstream fout("Sate.out");
struct nod
{
	int i;
	int j;
	int D;
};
int main()
{
	vector<nod> sate;
	int x, y, m, n;
	fin >> n;
	fin >> m;
	fin >> x;
	fin >> y;
	while (!fin.eof())
	{
		nod *p = new nod;
		fin >> p->i;
		fin >> p->j;
		fin >> p->D;
		sate.push_back(*p);
	}
	vector<nod>::const_iterator cii;
	int sc = x;
	int distanta = 0;
	cii = sate.begin();
	while (sc!=y)
	{
		if (sc == cii->i)
		{
			sc = cii->j;
			distanta += cii->D;
		}
		else if (sc==cii->j)
		{
			sc = cii->i;
			distanta -= cii->D;
		}
		cii++;
		if (cii == sate.end())
			cii = sate.begin();
	}
	fout << distanta;
	return 1;
}