#include <fstream>
#include <vector>
#include <queue>
#define MAX 30005
#define INF 1<<30

using namespace std;

struct nod{
    int nd, wt;
} dt;

vector<nod> v[MAX];
queue<int> q;
int n, m, x, y;
int d[MAX];

void read();
void bfs();
void write();

int main(){
    read();
    bfs();
    write();
    return 0;
}

void read(){
    ifstream fin ("sate.in");
    fin >> n >> m >> x >> y;
    int u, o, p;
    for (int i = 1; i <= n; ++i){
        fin >> u >> o >> p;
        if (u > o)
            swap(u, o);
        dt.nd = o, dt.wt = p;
        v[u].push_back(dt);
        dt.nd = u, dt.wt = -p;
        v[o].push_back(dt);
    }
    fin.close();
}

void bfs(){
    q.push(x);

    while(!q.empty()){
        int k = q.front();
        q.pop();

        for (unsigned int i = 0; i < v[k].size(); ++i)
            if (d[v[k][i].nd] == 0 && v[k][i].nd != x){
                d[v[k][i].nd] = d[k] + v[k][i].wt;
                q.push(v[k][i].nd);
                if (v[k][i].nd == y)
                    return;
            }
    }
}

void write(){
    ofstream fout ("sate.out");
    fout << (d[y] < 0 ? -d[y] : d[y]) << "\n";
    fout.close();
}