#include <fstream>
#define N 30002
#include <vector>
#include <deque>
#define INF 2000000000

using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");

struct bla
{
    int ve, co;
};
vector <bla> graph[N];
bool viz[N];
int dist[N];
deque <int> q;

int main()
{
    int n, m, x, y, X, Y, c, nod;
    f >> n >> m >> X >> Y;
    for (int i = 1;i <= m;++i)
    {
        f >> x >> y >> c;
        graph[x].push_back({ y,c });
        graph[y].push_back({ x,-c });
    }
    for (int i = 1;i <= n;++i) dist[i] = INF;
    q.push_back(Y);
    dist[Y] = 0;
    while (!q.empty())
    {
        nod = q.front();
        q.pop_front();
        if (viz[nod]) continue;
        viz[nod] = 1;
        for (int j = 0;j < graph[nod].size();++j)
        {
            int vee = graph[nod][j].ve;
            int cost = dist[nod] + graph[nod][j].co;
            if (!viz[vee])
            {
                dist[vee] = cost;///se stie ca distanta finala dinstre X si Y e unica
                q.push_back(vee);
            }
        }
    }
    g << -dist[X] << '\n';
    f.close();
    g.close();
    return 0;
}