#include <bits/stdc++.h>
#define INF 100000000

using namespace std;

ifstream fin("sate.in");

ofstream fout("sate.out");

queue<int> q;
vector<pair<int, int>> l[30005];
int n, m, start, stop, cost[30005];

void bfs()
{
    while (!q.empty())
    {
        int nod = q.front();
        q.pop();
        for (int i = 0; i < l[nod].size(); i++)
        {
            int vecin = l[nod][i].first;
            int c = l[nod][i].second;
            if (cost[vecin] == INF)
            {   cost[vecin] = cost[nod] + c;
                q.push(vecin);
            }
        }
    }
}
int main()
{
    fin >> n >> m >> start >> stop;
    q.push(start);
    for (int i = 1; i <= n; i++)
    {
        cost[i] = INF;
    }
    for (; m--;)
    {
        int x, y, c;
        fin >> x >> y >> c;
        l[x].push_back({y, c});
        l[y].push_back({x, -c});
    }
    bfs();
    fout << cost[stop]-INF;
}