#include<stdio.h>
#include<stdlib.h>
#include<queue>
#include<algorithm>
using namespace std;
#define mp make_pair
#define fs first
#define sc second
struct graf
{
	int n,d;
};
int n,m,x,y;
graf *a[30010];
int cat[30010];
void citire()
{
	scanf("%d%d%d%d",&n,&m,&x,&y);
	int n1,n2,d;
	for(; m; m--)
	{
		scanf("%d%d%d",&n1,&n2,&d);
		if((cat[n1]&7)==0)
			a[n1]=(graf*)realloc(a[n1],(cat[n1]+10)*sizeof(graf));
		if((cat[n2]&7)==0)
			a[n2]=(graf*)realloc(a[n2],(cat[n2]+10)*sizeof(graf));
		a[n1][cat[n1]].n=n2;
		a[n1][cat[n1]++].d=d;
		a[n2][cat[n2]].n=n1;
		a[n2][cat[n2]++].d=d;
	}
	if(x>y)
		swap(x,y);
}
void bfs()
{
	queue < pair<int,int> > q;
	q.push(mp(x,0));
	bool incoada[30010]={0};
	incoada[x]=true;
	pair<int,int> now;
	int i,next;
	while(!q.empty())
	{
		now=q.front();
		q.pop();
		for(i=0; i<cat[now.fs]; i++)
		{
			next=a[now.fs][i].n;
			if(next==y)
			{
				if(y>now.fs)
					printf("%d\n",now.sc+a[now.fs][i].d);
				else
					printf("%d\n",now.sc-a[now.fs][i].d);
				exit(0);
			}
			if(!incoada[next])
			{
				incoada[next]=true;
				if(next>now.fs)
					q.push(mp(next,now.sc+a[now.fs][i].d));
				else
					q.push(mp(next,now.sc-a[now.fs][i].d));
			}
		}
	}
}
int main()
{
	freopen("sate.in","r",stdin);
	freopen("sate.out","w",stdout);
	citire();
	bfs();
	return 0;
}