#include <fstream>
#include <vector>
#include <deque>
using namespace std;
ifstream fi("sate.in");
ofstream fo("sate.out");

#define NMAX 30001
#define pb push_back
#define mp make_pair
#define f first
#define s second

int n,m,x,y,i,auxa,auxb,auxd,viz[NMAX],rs;
vector< pair< int,int > > a[NMAX];
vector< pair< int,int > >::iterator itv;

deque< pair< int,int > > q;


int main(){
	
	fi >> n >> m >> x >> y;
	for (i=0; i<m; i++){
		fi >> auxa >> auxb >> auxd;
		a[auxa].pb(mp(auxb,auxd));
		a[auxb].pb(mp(auxa,auxd));
	}
	
	q.pb(mp(x,0)); viz[x]=1;
	int ok=1;
	while (ok){
		auxa=q.front().f; auxd=q.front().s; q.pop_front();
		for (itv=a[auxa].begin(); itv!=a[auxa].end(); itv++){
			if (!viz[(*itv).f]){
				if ((*itv).f==y){
					ok=0; 
					rs=auxd+((*itv).f<auxa?-1:1)*(*itv).s;
					break;
				}
				q.pb(mp((*itv).f,auxd+((*itv).f<auxa?-1:1)*(*itv).s));
				viz[(*itv).f]=1;
			}
			
		}
		
	}
	
	fo << rs;
	
	return 0;
}