#include <bits/stdc++.h>

using namespace std;

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

const int NMAX = 30005;



int main()
{
    int n, m, start, stop, cost[NMAX];
    fin >> n >> m >> start >> stop;

    queue<int> q;
    q.push(start);
    for (int i = 1; i <= n; i++)
    {
        cost[i] = INT_MAX;
    }

    vector<vector<pair<int, int>>> v(NMAX);
    while (m--)
    {
        int x, y, c;
        fin >> x >> y >> c;
        v[x].emplace_back(y, c);
        v[y].emplace_back(x, -c);
    }

    while (!q.empty())
    {
        int nod = q.front();
        q.pop();
        for (int i = 0; i < v[nod].size(); i++)
        {
            int vecin = v[nod][i].first;
            int c = v[nod][i].second;
            if (cost[vecin] == INT_MAX)
            {
                cost[vecin] = cost[nod] + c;
                q.push(vecin);
            }
        }
    }

    fout << cost[stop] - INT_MAX;
}