//
// Created by Alex on 10/24/2026.
//
#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;

void bfs(queue<int> &noduri,vector<int> &distantaFinala, const vector<vector<pair<int,int>>>& graf , vector<bool>& in_queue ) {
        while (!noduri.empty()) {
            int nod=noduri.front();
            noduri.pop();
            in_queue[nod]=false;

            for (int j=0;j<graf[nod].size();j++) {
                int vecin=graf[nod][j].first;
                int cost=graf[nod][j].second;


                    if (cost+distantaFinala[nod]< distantaFinala[vecin]) {
                        distantaFinala[vecin]=cost+distantaFinala[nod];
                        if (!in_queue[vecin]) {
                             noduri.push(vecin);
                            in_queue[vecin]=true;
                        }



                    }
            }

        }



}



int main() {
    ifstream fin("sate.in");
    ofstream fout("sate.out");
    int n,m,s,f;
    fin>>n>>m>>s>>f;
    vector<int> distantaFinala(n+1,999999999);
    distantaFinala[s] = 0;
    vector<vector<pair<int,int>>> graf(n+1);
    for (int i=0;i<m;i++) {
        int nod1,nod2,dis;
        fin>>nod1>>nod2>>dis;
        graf[nod1].push_back({nod2,dis});
        graf[nod2].push_back({nod1, -dis});

    }
    queue<int> q;
    q.push(s);
    vector<bool> in_queue(n + 1, false);
    bfs(q, distantaFinala, graf,in_queue);
    fout<<distantaFinala[f];


}