#include <queue>
#include <iostream>
#include <vector>
#include <cstdio>
#include <stack>

#define INF -666013

using namespace std;

class AdjNode {
private:
    int _v;
    int _weight;
public:
    AdjNode(int v, int weight) {
        _v = v;
        _weight = weight;
    }
    int getNode() {
        return this->_v;
    }
    int getWeight() {
        return this->_weight;
    }
};

class Sate {

private:
    vector<AdjNode> *_adjList;
    int _nodesNr;
public:
    Sate(int V) {
        _nodesNr = V;
        _adjList = new vector<AdjNode>[_nodesNr + 2];
    }
    ~Sate() {
        delete[] _adjList;
    }

    void addEdge(int u, int v, int weight) {
        AdjNode node(v,weight);
        _adjList[u].push_back(node); 
    }


    int BFS(int src_node, int dst_node) {
        int cost = 0;
        bool *visited = new bool[this->_nodesNr + 2];

        for(int i = 1; i <= this->_nodesNr + 2; ++i) {
            visited[i] = false;
        }
        queue<int> Q;
        visited[src_node] = true;
        Q.push(src_node);

        while(!Q.empty()) {

            int node = Q.front(); Q.pop();

            for(vector<AdjNode>::iterator it = _adjList[node].begin(); it != _adjList[node].end(); ++it) {

                if(!visited[it->getNode()]) {
                    visited[it->getNode()] = true;
                    Q.push(it->getNode());
                    cost += it->getWeight();
                    if(it->getNode() == dst_node) {

                        return cost;
                    }
                }
            }
        }
        return INF;
    }
};

int main(int argc, char const *argv[])
{
	FILE *f, *fwr;

	if((f = fopen("sate.in","r")) == NULL) {
		fprintf(stderr, "Can't open file!\n");
		return 0;
	}
	fwr = fopen("sate.out", "w");
	int N, M, X, Y, x, y, w;

    fscanf(f,"%d %d %d %d", &N, &M, &X, &Y);
//	fscanf(f, "%d %d", &N, &M);
    //cout << N << ' ' << M << ' ' << X << ' ' << Y << endl;
    Sate g(N);

    for(int i = 0 ; i < M; i++) {

        fscanf(f,"%d %d %d", &x, &y, &w);
        g.addEdge(x,y,w);
        g.addEdge(y,x,-w);
    }
    
   // cout << g.BFS(X,Y) << endl;
    fprintf(fwr, "%d\n", g.BFS(X,Y));
    fclose(f);
    fclose(fwr);


	return 0;
}