#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
int distmin[30001];
bool cc(int& a,int& b)
{
	if (distmin[a] <= distmin[b]) { return false; }
	return true;
}
int main()
{
	ifstream in("sate.in");
	ofstream out("sate.out");
	register int i, n, m, x, y,a,b,c;
	vector<pair<int,int> > d[30001];
	vector<int> gramada;
	in >> n;
	in >> m;
	in >> x;
	in >> y;
	for (i = 1;i <= m;i++)
	{
		in >> a;
		in >> b;
		in >> c;
		d[a].push_back(make_pair(b, c));
		d[b].push_back(make_pair(a, -c));
	}
	for (i = 1;i <= n;i++)
	{
		distmin[i] = 9999999;
	}
	distmin[x] = 0;
	gramada.push_back(x);
	while (!gramada.empty())
	{
		b = gramada[0];
		pop_heap(gramada.begin(), gramada.end(), cc);
		gramada.pop_back();
		for (i = 0;i < d[b].size();i++)
		{
			if (distmin[d[b][i].first]>distmin[b] + d[b][i].second)
			{
				distmin[d[b][i].first] = distmin[b] + d[b][i].second;
				gramada.push_back(d[b][i].first);
			}
			make_heap(gramada.begin(), gramada.end());
		}
	}
	out << distmin[y];
}