#include <fstream>
#include <vector>
#include <queue>
#include <algorithm>
#include <stack>

using namespace std;

fstream fin("sate.in", ios::in);
fstream fout("sate.out", ios::out);

#define MAXDIM 30005
pair <int, int> exe;
vector <pair<int, int>> list[MAXDIM];
int final_dist;
bool used[MAXDIM];

void read()
{
	int x, y, m, c, n;
	fin >> n >> m >> x >> y;
	exe.first = x; exe.second = y;
	for (int i = 1; i <= m; i++){
		fin >> x >> y >> c,
		list[x].push_back(make_pair(y, c)),
		list[y].push_back(make_pair(x, c));
	}
	fin.close();
}
void BFS()
{
	queue <pair<int, int>> q;
	q.push(make_pair(exe.first, 0));

	while (!q.empty()){
		pair <int, int> node = q.front(), new_node;
		q.pop();
		if (node.first == exe.second) { final_dist = node.second; return; }
		used[node.first] = true;

		for (int i = 0, size = list[node.first].size(); i < size; i++){
			new_node = list[node.first][i];
			if (used[new_node.first]) continue;
			q.push(make_pair(new_node.first, new_node.first > node.first ? node.second + new_node.second : node.second - new_node.second));
		}
	}
}

int main()
{
	read();
	BFS();
	fout << final_dist << "\n";

	fout.close();
	return 0;
}