#include <bits/stdc++.h>

using namespace std;

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

const int INF = 1e9;
const int NMAX = 3e4;

int N, M, X, Y;
int dist[NMAX + 1];
vector<pair<int, int>> edges[NMAX + 1];

void dfs(int node0) {
	for(auto &edge: edges[node0]) {
		if(dist[edge.first] == INF) {
			dist[edge.first] = dist[node0] + edge.second;
			dfs(edge.first);
		}
	}
}

int main() {
	fin >> N >> M >> X >> Y;

	for(int i = 1; i <= M; i++) {
		int x, y, c;
		fin >> x >> y >> c;

		edges[x].push_back({y, c});
		edges[y].push_back({x, -c});
	}

	for(int i = 1; i <= N; i++) {
		dist[i] = INF;
	}
	dist[X] = 0;

	dfs(X);

	fout << dist[Y] << '\n';
	return 0;
}