#include <bits/stdc++.h>
#define F first
#define S second

using namespace std;

int n,m,x,y;
bool V[30010];
vector <pair<int,int> > A[30010];

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

int BFS(int x, int y){
	queue <pair<int,int> > q;
	q.push({x,0});
	int pn=0,s=0;
	while(!q.empty()){
		int cn=q.front().F;
		if(cn<pn)s-=q.front().S;
		else s+=q.front().S;
		if(cn==y)return s;
		for(int i=0;i<A[cn].size();i++){
			if(!V[A[cn][i].F])q.push({A[cn][i].F,A[cn][i].S});
		}
		V[cn]=1;
		q.pop();
		pn=cn;
	}	
}

int main(){
	fin>>n>>m>>x>>y;
	memset(V,0,n);
	for(int i=0;i<m;i++){
		int xc,yc,vc;
		cin>>xc>>yc>>vc;
		A[xc].push_back({yc,vc});
		A[yc].push_back({xc,vc});
	}
	fout<<BFS(x,y);
	return 0;
}