#include <iostream>
#include <fstream>
#include <vector>
#include <queue>

using namespace std;

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

const int MAXN = 30010;

vector < pair <int, int> > Graf[MAXN];
queue <int> Q;
int Cost[MAXN];
bool Viz[MAXN];

int main()
{
    int N, M, X, Y, a, b, c, i;
    vector < pair <int, int> > :: iterator it;
    int nod;

    in >> N >> M >> X >> Y;

    while (M --){
        in >> a >> b >> c;

        Graf[a].push_back (make_pair (b, c));
        Graf[b].push_back (make_pair (a, -c));
    }

    for (i = 1; i <= N; i ++){
        Viz[i] = 0;
        Cost[i] = (1 << 30);
    }

    Q.push (X);
    Cost[X] = 0;

    while (!Q.empty ()){
        nod = Q.front ();
        Q.pop ();
        Viz[nod] = 0;

        for (it = Graf[nod].begin (); it != Graf[nod].end (); ++ it)
            if (Cost[nod] + (it -> second) < Cost[it -> first]){
                Cost[it -> first] = Cost[nod] + (it -> second);

                if (it -> first == Y){
                    out << Cost[it -> first];

                    return 0;
                }

                if (!Viz[it -> first]){
                    Q.push (it -> first);
                    Viz[it -> first] = 1;
                }
            }
    }

    return 0;
}