#include<fstream>
#include<iostream>
#include<vector>
#include<queue>
using namespace std;

int BFS(vector<vector<pair<unsigned short,int> > >& graph,
		unsigned short n,
		unsigned short start,
		unsigned short end)
{
	queue<pair<unsigned short,int> > Q;
	Q.push(make_pair(start,0));
	vector<bool> visited;
	visited.resize(n+1);
	
	while(!Q.empty())
	{
		unsigned short node=Q.front().first;
		int dist=Q.front().second;
		Q.pop();
		if(node==end)
			return dist;
		for(int i=0; i<(int)graph[node].size(); ++i)
		{
			if(!visited[graph[node][i].first])
			{
				visited[graph[node][i].first]=true;
				if(graph[node][i].first<node)
				{
					Q.push(make_pair(graph[node][i].first,dist-graph[node][i].second));
				}
				else
				{
					Q.push(make_pair(graph[node][i].first,dist+graph[node][i].second));
				}
			}
		}
	}
	return n;
}

int main()
{
	unsigned short n,st,end,x,y;
	int m,c;
	fstream fin("sate.in", fstream::in);
	fstream fout("sate.out", fstream::out);
	vector<vector<pair<unsigned short,int> > > graph;
	fin>>n>>m>>st>>end;
	//cout<<n<<" "<<m<<" "<<st<<" "<<end<<endl;
	graph.resize(n+1);
	for(int i=0; i<m; ++i)
	{
		fin>>x>>y>>c;
		graph[x].push_back(make_pair(y,c));
		graph[y].push_back(make_pair(x,c));
	}
	
	/*for(int i=1; i<=n; ++i)
	{
		cout<<i<<": ";
		for(int j=0; j<(int)graph[i].size(); ++j)
		{
			cout<<graph[i][j].first<<" ";
		}
		cout<<endl;
	}*/
	
	fout<<BFS(graph,n,st,end)<<endl;
	
	fin.close();
	fout.close();
	return 0;
}