#include <bits/stdc++.h>

std::vector<int> vizitat;
std::vector<std::vector<std::pair<int,int>>> graf;
std::queue<int> q; std::vector<int> cost;

void bfs(int n) { 


        q.push(n);
        vizitat[n] = 1; cost[n] = 0;
        
        while (!q.empty()) {
            int nod = q.front(); q.pop();

            for (auto [a, b] : graf[nod]) {
 
                if (!vizitat[a]) {
                    vizitat[a] = 1;
                    cost[a] = cost[nod] + b;
                    q.push(a);
                }
            }
        }
       
}


int main(){
    int n, m, x, y;
    std::ifstream fin("sate.in");
    std::ofstream fout("sate.out");
    fin >> n >> m >> x >> y;
        graf.resize(n + 1);
        vizitat.assign(n + 1, false);
        cost.assign(n + 1, 0);

    
    for (int i = 0; i < m; i++) {
        int a, b, c;
        fin >> a >> b >> c;
        graf[a].push_back({b, c});
        graf[b].push_back({a, -c});
    }

       

        
        bfs(x);
        fout << std::abs(cost[y]);
}