#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];
pair<int,int> p;

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

int BFS(int x, int y){
	queue <pair<int,int> > q;
	p.F=x;p.S=0;
	q.push(p);
	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]);
		}
		V[cn]=1;
		if(!q.empty())q.pop();
		pn=cn;
	}	
	return s;
}

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;
		p.F=yc;p.S=vc;
		A[xc].push_back(p);
		p.F=xc;
		A[yc].push_back(p);
	}
	fout<<BFS(x,y);
	return 0;
}