#include <bits/stdc++.h>
#define MAXN 30010
#define ll long long
#define pii pair<int,ll>
#define vii vector<pii>
#define F first
#define S second
using namespace std;

int n,m,x,y;
vii A[MAXN];
bool V[MAXN];

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

void DFS(int c,int d){
	if(c==y){
		fout<<d;
		exit(0);
	}
	V[c]=1;
	for(int i=0;i<A[c].size();i++){
		if(!V[A[c][i].F]){
			DFS(A[c][i].F,d+A[c][i].S);
		}	
	}
}

int main(){
	fin>>n>>m>>x>>y;
	for(int i=0;i<m;i++){
		int a;
		pii p;
		fin>>a>>p.F>>p.S;
		A[a].push_back(p);
		swap(a,p.F);
		p.S=-p.S;
		A[a].push_back(p);
	}
	DFS(x,0);
	return 0;
}