#include <bits/stdc++.h>
#define nmax 30005
using namespace std;

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


int n,m,x,y,l,r,w;
int dist=0;
bool viz[nmax];
vector<pair<int,int>> adj[nmax];

void dfs(int nod, int &rasp) {
    viz[nod]=1;
    if (nod==y) return;

    for (int j=0;j<adj[nod].size();j++) {
        if (!viz[adj[nod][j].second])
            rasp+=adj[nod][j].first, dfs(adj[nod][j].second, rasp);
    }
}
int main() {
    f>>n>>m>>x>>y;
    for (int i=1;i<=m;i++) {
        f>>l>>r>>w;
        adj[l].push_back({w,r});
        adj[r].push_back({-w,l});
    }
    dfs(x,dist);
    g<<dist;
    return 0;
}