#include <fstream>
#include <vector>
#include <queue>
using namespace std;

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

int main() {
    int n, m, x, y;
    fin >> n >> m >> x >> y;

    // lista de adiacenta: (vecin, cost cu semn)
    vector<vector<pair<int, int>>> cost(n + 1);

    for (int k = 0; k < m; k++) {
        int i, j, d;
        fin >> i >> j >> d;
        cost[i].push_back({j, d});    // P[j] = P[i] + d
        cost[j].push_back({i, -d});   // P[i] = P[j] - d
    }

    vector<long long> P(n + 1, 0);
    vector<bool> vis(n + 1, false);

    queue<int> q;
    q.push(x);
    vis[x] = true;
    P[x] = 0;

    while (!q.empty() && !vis[y]) {
        int u = q.front();
        q.pop();
        for (auto &e : cost[u]) {
            int v = e.first;
            int c = e.second;
            if (!vis[v]) {
                vis[v] = true;
                P[v] = P[u] + c;
                q.push(v);
            }
        }
    }

    long long raspuns = P[y] - P[x];
    if (raspuns < 0) raspuns = -raspuns;
    fout << raspuns << "\n";

    return 0;
}