#include <iostream>
#include<fstream>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n, m, viz[30001], cnt ,xx ,yy;
double costt ;
double numar;
typedef struct nod
{
    int x;
    double cost;
    nod *a;
} *pNod;
pNod v[30001];

void add(pNod &dest, int val,double c)
{
    pNod p;
    p=new nod;
    p->x=val;
    p->cost=c;
    p->a=dest;
    dest=p;
}

void citire()
{
    f>>n>>m;
    int i, x, y;
    double c;
    f>>xx>>yy;
    for (i=1;i<=m;i++)
    {
        f>>x>>y>>c;
        add(v[x],y,c);
        add(v[y],x,c);

    }
}
void DF(int nod)
{
    pNod p;
    if (nod==yy)
    {
        g<<costt;

    }
    else {
    viz[nod] = 1;
for (p=v[nod];p!=NULL;p=p->a)
    {
        if (!viz[p->x])
        if (p->x<nod)
        {
            costt-=p->cost;
            DF(p->x);
           // costt+=p->cost;
        }
        else
        {
            costt+=p->cost;
            DF(p->x);
           // costt-=p->cost;
        } }
}
}
int main()
{   // int k;
    citire();
  //  int i;
    DF(xx);
  //  printf("%d\n",cnt);
    //g<<costt;
}