#include <iostream>
#include <fstream>
#define nmax 30001
#include <queue>
#include <vector>

using namespace std;

ifstream fin("sate.in");
ofstream fout("sate.out");

int d[nmax];
int n, m;
int x, y;
bool viz[nmax];

vector < pair < int,int  > > muchii[nmax];

void citeste()
{
    fin >> n >> m >> x >> y;
    for (int i = 1; i<= m; i++)
    {
        int a, b, c;
        fin >> a >> b >> c;
        muchii[a].push_back(make_pair(b,c));
        muchii[b].push_back(make_pair(a,-c));
    }
}

int bfs(int nodstart,int nodfinal)
{
    int nod = nodstart;
    viz[nod] = true;
    int s = 0;
    while (nod!=nodfinal)
    {
        for (unsigned int i = 0;i < muchii[nod].size(); i++)
        {
            int vecin = muchii[nod][i].first;
            int dist = muchii[nod][i].second;
            if (!viz[vecin])
            {
                s += dist;
                viz[vecin] = true;
                nod = vecin;
            }
        }
    }
    return s;
}

int main()
{
    citeste();
    fout << bfs(x,y);
    return 0;
}