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

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

int n, m, X, Y;
int d[30005];
vector<pair<int, int>> L[30005];
queue<int> q;

void BFS(int k)
{
    for (int i = 1; i <= n; i++)
        d[i] = 2e9;
    d[k] = 0;
    q.push(k);
    while (!q.empty())
    {
        k = q.front();
        q.pop();
        for (auto w : L[k])
            if (d[w.first] > d[k] + w.second)
            {
                d[w.first] = d[k] + w.second;
                q.push(w.first);
            }
    }
}

int main()
{   
    int i, j, c;
    fin >> n >> m >> X >> Y;
    while (m--)
    {
        fin >> i >> j >> c;
        L[i].push_back({j, c});
        L[j].push_back({i, -c});
    }
    BFS(X);
    fout << d[Y] << "\n";
}