#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <cmath>
using namespace std;
ifstream fi("sate.in");
ofstream fo("sate.out");
int n;
int m;
vector <pair<int,int> >V[30001];
int DFS(int parent,int nodeS,int nodInt,int d,int destinatie,int &sol)
{
    for(int i=0;i<V[nodInt].size();i++)
    {
        int vecin=V[nodInt][i].first;
        if(vecin==parent)
            continue;
        if(vecin==destinatie)
        {
            sol=d+V[nodInt][i].second;
        }else
        {
            if(vecin>nodInt)
                DFS(nodInt,nodeS,vecin,d+V[nodInt][i].second,destinatie,sol);
            else
                DFS(nodInt,nodeS,vecin,abs(d-V[nodInt][i].second),destinatie,sol);
        }
    }
}
int main()
{
    fi>>n>>m;
    int nodeStart,nodeFinish;
    fi>>nodeStart>>nodeFinish;
    for(int i=1;i<=m;i++)
    {
        int x,y,D;
        fi>>x>>y>>D;
        V[x].push_back(make_pair(y,D));
        V[y].push_back(make_pair(x,D));
    }
    int rez;
    DFS(0,nodeStart,nodeStart,0,nodeFinish,rez);
    fo<<rez;
    return 0;
}