#include <iostream>
#include <fstream>
#include <queue>
#include <vector>
#include <cmath>
#define INF 2e9

using namespace std;

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

int n, m, X, Y;
vector<vector<pair<int, int>>> adj;
vector<int> dist;

void BFS(int source) {
    queue<int> q;
    q.push(source);
    dist[source] = 0;
    while (!q.empty()) {
        int nod = q.front();
        q.pop();
        for (auto [i, D] : adj[nod])
            if (dist[i] > dist[nod] + D || dist[i] > dist[nod] - D) {
                if (nod < i)
                    dist[i] = dist[nod] + D;
                else
                    dist[i] = dist[nod] - D;
                q.push(i);
            }
    }
}

int main()
{
    fin >> n >> m >> X >> Y;
    adj.resize(n + 5);
    dist.resize(n + 5);

    for (int i = 1; i <= n; i++)
        dist[i] = INF;

    for (int i = 1; i <= m; i++) {
        int x, y, D;
        fin >> x >> y >> D;
        adj[x].push_back({y,D});
        adj[y].push_back({x,D});
    }

    BFS(X);
    fout << dist[Y];
//    for (int i = 1; i <= n; i++)
//        cout << dist[i] << " ";
    return 0;
}