#include <bits/stdc++.h>
using namespace std;

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

// first = target, second = distance
vector<pair<int, int>> A[30001];
int visited[30001];
int N, M, X, Y, total_dist = 0;

bool dfs(int k) {
    int target, dist;
    visited[k] = 1;
    for (auto &p : A[k]) {
        if (!visited[p.first]) {
            target = p.first, dist = p.second;

            dist = target > k ? dist : -dist;
            total_dist += dist;
            
            if (target == Y || dfs(target))
                return true;

            total_dist -= dist;
        }
    }

    return false;
}

int main() {
    fin >> N >> M >> X >> Y;

    int x, y, d;
    for (int i = 0; i < M; i++) {
        fin >> x >> y >> d;
        A[x].push_back({y, d});
        A[y].push_back({x, d});
    }

    /*
        DFS(start = X/Y)
        +
        If target > current => total_distance += d(target, current)
        else if target < current -= d(target, current)

        te intorci din nivelul dfs si !found_Y(/X) => total_distance -= d(target, current)
    */

    if (dfs(X))
        // daca start (X) > end (Y) => -distanta
        fout << abs(total_dist);

    return 0;
}