#include <iostream>
#include <vector>
#include <queue>

using namespace std;

#define pb push_back
#define N 30030
#define INF 1e18
#define FILE "sate"

struct nod {
	int v;
	int w;
};

int n, m, from, to;
vector<nod> g[N];
int64_t dist[N];
queue<int> q;

int main() {
	freopen(FILE".in", "r", stdin);
	freopen(FILE".out", "w", stdout);
	cin >> n >> m >> from >> to;
	for(int i = 1; i <= m; i++) {
		int u, v, w;
		cin >> u >> v >> w;
		g[u].pb({v, w});
		g[v].pb({u, -w});
	}
	for(int i = 1; i <= n; i++) {
		dist[i] = INF;
	}
	dist[from] = 0;
	q.push(from);
	while(!q.empty()) {
		int u = q.front();
		q.pop();
		for(auto nod : g[u]) {
			if(dist[nod.v] == INF) {
				dist[nod.v] = nod.w + dist[u];
				q.push(nod.v);
			}
		}
	}
	cout << dist[to] << '\n';
}