#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>

using namespace std;

ifstream fin("sate.in");
ofstream fout("sate.out");

const int NMAX = 30001;

vector < pair < int, int > > V[NMAX]; // in first se memoreaza nodul adiacent, iar in second distanta pana la acel nod
int n, m, X, Y;
int D[NMAX];

void read()
{
    int i, x, y, d;
    fin >> n >> m >> X >> Y;
    for (i = 1; i <= m; ++ i)
        {
         fin >> x >> y >> d;
         // se construieste graful
         V[x].push_back(make_pair(y, d));
         V[y].push_back(make_pair(x, -d));
        }
}

void bfs(int source)
{
    // bfs
    queue < int > Q;
    vector < pair < int, int > > :: iterator it;
    int nod;
    bool viz[NMAX] = {false};
    Q.push(source); // se adauga nodul de plecare in coada
    viz[source] = true; // se marcheaza nodul de plecare ca fiind vizitat
    while (!Q.empty())
        {
         nod = Q.front();
         Q.pop();
         for (it = V[nod].begin(); it < V[nod].end(); ++ it) // se parcug nodurile adiacente
            if (!viz[(*it).first] || D[nod] + (*it).second < D[(*it).first])
                {
                 // daca un nod adaicent nu a mai fost vizitat sau se afla la o distanta mai mica
                 Q.push((*it).first); // se adauga in coada
                 viz[(*it).first] = true; // se marcheaza ca vizitat
                 D[(*it).first] = D[nod] + (*it).second; // se actualizeaza distanta
                }
        }
}

int main()
{
    read();
    fin.close();
    bfs(X); // bfs de la nodul de plecare
    fout << D[Y] << "\n"; // se afiseaza distanta dintre noduri
    fout.close();
    return 0;
}