#include <iostream>
#include <fstream>
#include <vector>
#include <stdlib.h>

using namespace std;

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

int seen[40000], d = 0, y;

struct drumuri
{
    int vecin;
    int dis;
};

void BFS(int nod, vector <drumuri> v[40000])
{
    if(nod == y)
    {
        out << d;
        exit(0);
    }
    seen[nod] = -1;
    for(int j = 0; j < v[nod].size(); ++j)
    {
        if (seen[v[nod][j].vecin] == 0)
        {
            d += v[nod][j].dis;
            BFS(v[nod][j].vecin, v);
            d -= v[nod][j].dis;
        }
    }
}

int main()
{
    vector <drumuri> v[40000];
    int n, m, a, b, i, x, dist;
    in >> n >> m >> x >> y;
    for(i = 0; i < m; ++i)
    {
        in >> a >> b >> dist;
        drumuri dr = {b, dist};
        v[a].push_back(dr);
        drumuri dr2 = {a, -dist};
        v[b].push_back(dr2);
    }
    BFS(x, v);
    return 0;
}