#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
#include <cstdlib>
using namespace std;

struct node
{
	int at;
	int cost;
};

inline node mn (const int &at, const int &cost)
{
	node nod;
	nod.at = at;
	nod.cost = cost;
	return nod;
}

int main (int argc, char const *argv[])
{
	ifstream in ("sate.in");
	int n, m; in >> n >> m;
	int inceput, sfarsit; in >> inceput >> sfarsit;
	
	vector< vector<int> >	edges 		(n + 1),
							costs 		(n + 1);
	int x, y, c;
	while (in >> x >> y >> c)
	{
		edges[x].push_back (y);
		costs[x].push_back (c);
	}
	in.close ();
	
	/*
	cout << "From:\n";
	for (int i = 1; i <= n; i++)
	{
		cout << i << ": ";
		for (unsigned j = 0; j < edges[i].size (); j++)
			cout << edges[i][j] << ' ';
		cout << '\n';
	}
	*/
	
	for (int i = 1; i <= n; i++)
	{
		if (edges[i].size () > 1)
		{
			//cout << "I can infer from " << i << " that:\n";
			for (unsigned j = 0; j < edges[i].size (); j++)
			{
				for (unsigned k = j + 1; k < edges[i].size (); k++)
				{
					//cout << "Got " << edges[i][j] << ' ' << edges[i][k] << 
					//		' ' << abs (costs[i][j] - costs[i][k]) << '\n';
					edges[edges[i][j]].push_back (edges[i][k]);
					costs[edges[i][j]].push_back (abs (costs[i][j] - costs[i][k]));
				}
			}
		}
	}
	
	vector<bool> visited (n + 1);
	stack<node> stiva;
	stiva.push ( mn (inceput, 0) );
	visited[inceput] = true;
	
	while (!stiva.empty ())
	{
		node nod = stiva.top ();
		stiva.pop ();
		
		if (nod.at == sfarsit)
		{
			ofstream out ("sate.out");
			out << nod.cost << '\n';
			out.close ();
			exit (0);
		}
		
		for (unsigned i = 0; i < edges[nod.at].size (); i++)
		{
			if (!visited[edges[nod.at][i]])
			{
				stiva.push ( mn (edges[nod.at][i], nod.cost + costs[nod.at][i]) );
				visited[edges[nod.at][i]] = true;
			}
		}
	}
	
	return 0;
}