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

int n, m, start, finish, dist[30001];
vector<pair<int, int>> v[30001];
queue<int> q;

int main()
{
    fin >> n >> m >> start >> finish;

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

    for(int i = 1; i<=n; ++i)
        dist[i] = 1<<30;

    q.push(start);
    dist[start] = 0;

    while(!q.empty())
    {
        int x = q.front();
        q.pop();

        for(int i=0; i<v[x].size(); ++i)
            if(dist[v[x][i].first] > dist[x] + v[x][i].second)
            {
                dist[v[x][i].first] = dist[x] + v[x][i].second;
                q.push(v[x][i].first);
            }
    }

    fout << dist[finish];

    return 0;
}