#include <stdio.h>
#include <vector>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#include <queue>
#define maxn 30005
#define oo 200000000
using namespace std;

int i,N,M,X,Y;
vector< pair<int,int> > A[maxn];
vector< pair<int,int> > :: iterator it;
queue<int> Q;
int v[maxn],D[maxn];

void citire()
{
	int x,y,z,aux;
	scanf("%d %d %d %d",&N,&M,&X,&Y);
	if(X>Y)
	{
		aux=X; X=Y; Y=aux;
	}
	for(i=1;i<=M;i++)
	{
		scanf("%d %d %d",&x,&y,&z);
		A[x].pb(mp(y,z));
		A[y].pb(mp(x,-z));
	}
}

void BF()
{
	int k;
	for(i=1;i<=N;i++) D[i]=oo;
	Q.push(X); v[X]=1; D[X]=0;
	for(;!Q.empty();Q.pop())
	{
		k=Q.front();
		for(it=A[k].begin();it!=A[k].end();it++)
			if(D[k]+it->ss<D[it->ff])
			{
				D[it->ff]=D[k]+it->ss;
				if(it->ff==Y) return;
				if(!v[it->ff])
				{
					v[it->ff]=1;
					Q.push(it->ff);
				}
			}
		v[k]=0;
	}
}

int main()
{
	freopen("sate.in","r",stdin);
	freopen("sate.out","w",stdout);
	citire();
	BF();
	printf("%d",D[Y]);
}