#include <iostream>
#include <fstream>
#include <vector>
#define NMAX 100100
using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
 
int n, m, x, y, size, minim = NMAX, sum, frecv[NMAX];
vector< pair<int, int> > gr[NMAX];
vector<int> v, f;
bool viz[NMAX];
 
void citire() {
  fin >> n >> m >> x >> y;
  for (int i = 1; i <= m; i++) {
    int a, b, cost;
    fin >> a >> b >> cost;
    gr[a].push_back(make_pair(b, cost));
    gr[b].push_back(make_pair(a, -1 * cost));
  }
}
 
void DFS(int n_start) {
  if (n_start == y)
    return;
  viz[n_start] = true;
  for (int i = 0; i < gr[n_start].size(); i++) {
    int comp = gr[n_start][i].first;
    int cost = gr[n_start][i].second;
    if (!viz[comp]) {
      sum += cost;
      DFS(comp);
    }
  }
}

void comp() {
  for (int i = 1; i <= n; i++)
    if (!viz[i])
      DFS(i);
}
 
int main(int argc, const char * argv[]) {
  citire();
  DFS(x);
  fout << sum;
}