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

using namespace std;

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

const int max_size = 3e4 + 1, INF = 1e9 + 1;

int d[max_size], viz[max_size];
vector <pair <int, int>> edges[max_size];

struct cmp{
    bool operator()(int x, int y)
    {
        return d[x] > d[y];
    }
};

priority_queue <int, vector <int>, cmp> pq;

void djk (int nod)
{
    viz[nod] = 1;
    d[nod] = 0;
    pq.push(nod);
    while (!pq.empty())
    {
        nod = pq.top();
        pq.pop();
        viz[nod] = 0;
        for (auto f : edges[nod])
        {
            if (d[nod] + f.second < d[f.first])
            {
                d[f.first] = d[nod] + f.second;
                if (viz[f.first] == 0)
                {
                    viz[f.first] = 1;
                    pq.push(f.first);
                }
            }
        }
    }
}

int main ()
{
    int n, t, x, y;
    in >> n >> t >> x >> y;
    while (t--)
    {
        int a, b, c;
        in >> a >> b >> c;
        edges[a].push_back({b, c});
        edges[b].push_back({a, -c});
    }
    for (int i = 1; i <= n; i++)
    {
        d[i] = INF;
    }
    djk(x);
    out << d[y];
    in.close();
    out.close();
    return 0;
}