#include <bits/stdc++.h>
using namespace std;
ifstream fin ("sate.in");
ofstream fout ("sate.out");

int n, m;
vector <pair <int, int>> g[100001];
int dist[100001];

void bfs(int sursa)
{
    dist[sursa] = 0;
    queue <pair <int, int>> q;
    q.push({sursa, 0});
    while (!q.empty())
    {
        int nod = q.front().first;
        q.pop();
        for (auto vecin : g[nod])
            if (!dist[vecin.first])
            {
                if (vecin.first < nod)
                    dist[vecin.first] = dist[nod] - vecin.second;
                else
                    dist[vecin.first] = dist[nod] + vecin.second;
                q.push(vecin);
            }
    }
}

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

    for (int i = 1; i <= m; i++)
    {
        int a, b, cost;
        fin >> a >> b >> cost;
        g[a].push_back({b, cost});
        g[b].push_back({a, cost});
    }
    bfs(x);
    fout << dist[y];
    return 0;
}