#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
vector <long long int> Nod[30001],Dist[30001];
long long int Distanta[30001],Coada[30001],noduri,muchi,start,fin,i,x,y,d;
bool Vizitat[30001];
int main()
{
    f>>noduri>>muchi>>start>>fin;
    for (i=0;i<muchi;i++)
    {
        f>>x>>y>>d;
        Nod[x].push_back(y);
        Dist[x].push_back(d);
        Nod[y].push_back(x);
        Dist[y].push_back(d);
    }
    Coada[0]=start;
    long long int k=0;
    long long int q=0;
    while (k<=q)
    {
        for (i=0;i<Nod[Coada[k]].size()&&k<=q;i++)
        {
            if (Nod[Coada[k]][i]==fin)
            {
                if (Coada[k]>Nod[Coada[k]][i])
                Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]-Dist[Coada[k]][i];
                else
                Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]+Dist[Coada[k]][i];
                g<<Distanta[Nod[Coada[k]][i]];
                k=q+10;
                return 0;
            }
            else if (Vizitat[Nod[Coada[k]][i]]==false)
            {
                q++;
                Vizitat[Nod[Coada[k]][i]]=true;
                Coada[q]=Nod[Coada[k]][i];
                if (Coada[k]>Nod[Coada[k]][i])
                Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]-Dist[Coada[k]][i];
                else
                Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]+Dist[Coada[k]][i];
            }
        }
        k++;
    }

}