#include<iostream>
#include<fstream>
#include<vector>
const int maxx=30002;
using namespace std;
int n,m,start,finish,i,a,b,c,inc,sf,coada[maxx][2];
bool viz[maxx];
vector <pair<int,int> > x[maxx];
void bfs()
{
	inc=sf=1;
	coada[inc][0]=start;
	while(inc<=sf)
	{
		viz[coada[inc][0]]=true;
		for(i=0;i<x[coada[inc][0]].size();i++)
			if(viz[x[coada[inc][0]][i].first]==false)
			{
				sf++;
				coada[sf][0]=x[coada[inc][0]][i].first;
				if(coada[inc][0]<x[coada[inc][0]][i].first)
					coada[sf][1]=coada[inc][1]+x[coada[inc][0]][i].second;
				else
					coada[sf][1]=coada[inc][1]-x[coada[inc][0]][i].second;
				if(finish==x[coada[inc][0]][i].first)
				{
					printf("%d\n",coada[sf][1]);
					i=x[coada[inc][0]].size()+5;
					inc=sf+5;
				}
			}
		inc++;
	}
}
int main()
{	
	freopen("sate.in","r",stdin);
	freopen("sate.out","w",stdout);
	scanf("%d %d %d %d\n",&n,&m,&start,&finish);
	for(i=1;i<=m;i++)
	{
		scanf("%d %d %d\n",&a,&b,&c);
		x[a].push_back(make_pair(b,c));
		x[b].push_back(make_pair(a,c));
	}
	bfs();
	return 0;
}