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

using namespace std;

const int NMAX = 30005;
vector<pair<int, int>> g[NMAX];
int d[NMAX], n, m, x, y;
bool viz[NMAX];

void BFS(int nod) {
    queue<int> q;
    q.push(nod); viz[nod] = true;
    while (!q.empty()) {
        int a = q.front(); q.pop();
        if (a == y) return;
        for (auto [i, j] : g[a])
            if (!viz[i]) viz[i] = true, d[i] = d[a] + j, q.push(i);
    }
}

int main() {
    ifstream fin("sate.in"); ofstream fout("sate.out");
    fin >> n >> m >> x >> y;
    for (int i = 0, a, b, c; i < m; ++i)
        fin >> a >> b >> c, g[a].push_back({b, c}), g[b].push_back({a, -c});
    BFS(x);
    fout << abs(d[y]) << "\n";
}