#include<iostream>
#include<deque>
#include<vector>
#include<cstring>
#define INF 0x7f
using namespace std;

vector<vector<int>> graph[2501];
vector<int> a;
int n, m, s, t, dis[2501], pre[2501], f1, f2, w, u, v;
bool exist[2501];
deque<int> team;

int main(){
	ios::sync_with_stdio(false);
	
	memset(dis, INF, sizeof(dis));
	memset(exist, false, sizeof(exist));
	cin >> n >> m >> s >> t;
	for(int i = 0;i < m;i++){
		cin >> f1 >> f2 >> w;
		a.clear();
		a.push_back(f2);
		a.push_back(w);
		graph[f1].push_back(a);
		a.clear();
		a.push_back(f1);
		a.push_back(w);
		graph[f2].push_back(a);
	}
	dis[s] = 0;
	team.push_back(s);
	exist[s] = true;
	do{
		u = team[0];
		team.pop_front();
		for(int i = 0;i < graph[u].size();i++){
			v = graph[u][i][0];
			if(dis[v] > dis[u]+graph[u][i][1]){
				dis[v] = dis[u]+graph[u][i][1];
				pre[v] = u;
				if(!exist[v]){
					team.push_back(v);
					exist[v] = true;
				}
			}
		}
		
	}while(!team.empty());
	cout << dis[t] << endl;
	return 0;
}

脑回路太清奇导致无法套用其他犇犇在题解里的算法 求教