#include <iostream>
#include <vector>
#include <queue>
#include <limits>

using namespace std;

struct Edge {
    int from;
    int to;
    int weight;
};

int main() {
    int N, M, S, T;
    cin >> N >> M >> S >> T;

    vector<vector<Edge>> graph(N + 1);

    for (int i = 0; i < M; i++) {
        int a, b, w;
        cin >> a >> b >> w;
        graph[a].push_back({a, b, w});
    }

    vector<int> dist(N + 1, numeric_limits<int>::max());
    dist[S] = 0;

    priority_queue<pair<int, int>, vector<pair<int, int>>, greater<>> pq;
    pq.push({0, S});

    while (!pq.empty()) {
        int current_dist = pq.top().first;
        int current_vertex = pq.top().second;
        pq.pop();

        if (current_dist > dist[current_vertex]) continue;

        for (const Edge& edge: graph[current_vertex]) {
            int new_dist = current_dist + edge.weight;
            if (new_dist < dist[edge.to]) {
                dist[edge.to] = new_dist;
                pq.push({new_dist, edge.to});
            }
        }
    }

    if (dist[T] == numeric_limits<int>::max()) {
        cout << -1 << endl;
    } else {
        cout << dist[T] << endl;
    }

    return 0;
}