#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <fstream>
#include <iterator>
#include <assert.h>
using namespace std;


const string file = "sate";

const string infile = file + ".in";
const string outfile = file + ".out";

const int INF = 0x3f3f3f3f;

int Solve(vector<vector<pair<int, int> > >& G, int N, int s, int t)
{
	vector<bool> viz(N + 1);
	queue<pair<int, int> > que;

	que.push(make_pair(s, 0));
	viz[s] = true;


	while(que.empty() == false)
	{
		pair<int, int> c = que.front();
		que.pop();

		int x = c.first;
		int d = c.second;

		if(x == t)
		{
			return d;
		}

		for(vector<pair<int, int> >::iterator itr = G[x].begin();
			itr != G[x].end();
			itr++)
		{
			if(viz[itr->first] == false)
			{
				viz[itr->first] = true;

				int newD = 0;
				if(itr->first > x)
				{
					newD = d + itr->second;
				}
				else
				{
					newD = d - itr->second;
				}

				que.push(make_pair(itr->first, newD));
			}
		}
	}


	return 0;
}


int main()
{
#ifdef ONLINE_JUDGE
	ostream &fout = cout;
	istream &fin = cin;
#else
	fstream fout(outfile.c_str(), ios::out);
	fstream fin(infile.c_str(), ios::in);
#endif	
	

	int N, M;
	int s, t;
	fin >> N >> M >> s >> t;

	vector<vector<pair<int, int> > > G;
	G.resize(N + 1);


	for(int i = 0; i < M; i++)
	{
		int x, y, c;
		fin >> x >> y >> c;
		G[x].push_back(make_pair(y, c));
		G[y].push_back(make_pair(x, c));
	}

	if(s > t)
	{
		swap(s, t);
	}
	fout << Solve(G, N, s, t) << "\n";



#ifdef ONLINE_JUDGE
#else

	fin.close();
	fout.close();
#endif
}