#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

const int NB_MAX_NOEUDS = 1000;
const int INFINI = 1000*1000*1000;
const int INDEFINI = -INFINI;

struct arrete
{
    int idNoeudArrive;
    int poidsArrete;

    arrete() {}
    arrete(int idNoeudArrive, int poidsArrete) : idNoeudArrive(idNoeudArrive), poidsArrete(poidsArrete) {}
};

struct noeud
{
    int idNoeud;
    int dist;

    noeud() {}
    noeud(int idNoeud, int dist) : idNoeud(idNoeud), dist(dist) {}

    bool operator < (const noeud &autre) const
    {
        return dist < autre.dist;
    }
};

struct Distance
{
    int dist;
    int idPere;

    Distance() {}
    Distance(int dist, int idPere) : dist(dist), idPere(idPere) {}
};

vector<arrete> voisinDuNoeud[NB_MAX_NOEUDS+2];
priority_queue<noeud> noeudsAVisiter;
Distance dist[NB_MAX_NOEUDS+2];

int nbNoeuds, nbArretes, noeudDepart, noeudArrive;

void initDist()
{
    for(int iCase = 0 ; iCase < NB_MAX_NOEUDS+2 ; iCase++)
        dist[iCase].dist = INDEFINI;
}

int main()
{
    scanf("%d%d%d%d", &nbNoeuds, &nbArretes, &noeudDepart, &noeudArrive);
    initDist();
    for(int iArrete = 0 ; iArrete < nbArretes ; iArrete++)
    {
        int noeud1, noeud2, poids;
        scanf("%d%d%d", &noeud1, &noeud2, &poids);
        voisinDuNoeud[noeud1].push_back(arrete(noeud2, poids));
        voisinDuNoeud[noeud2].push_back(arrete(noeud1, poids));
    }

    noeudsAVisiter.push(noeud(noeudDepart, 0));

    while(!noeudsAVisiter.empty())
    {
        int idNoeudEnCours = noeudsAVisiter.top().idNoeud;
        int distNoeudEnCours = noeudsAVisiter.top().dist;

        if(dist[idNoeudEnCours].dist == INDEFINI)
        {
            dist[idNoeudEnCours].dist = distNoeudEnCours;
            if(idNoeudEnCours == noeudDepart)
                dist[idNoeudEnCours].dist = 0;
            for(int iVoisin = 0 ; iVoisin < voisinDuNoeud[idNoeudEnCours].size() ; iVoisin++)
            noeudsAVisiter.push(noeud(voisinDuNoeud[idNoeudEnCours][iVoisin].idNoeudArrive, dist[idNoeudEnCours].dist+voisinDuNoeud[idNoeudEnCours][iVoisin].poidsArrete));
            noeudsAVisiter.pop();
        }
        else
            noeudsAVisiter.pop();

    }

    printf("%d\n", dist[noeudArrive].dist);

}