#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
vector <int> Nod[30001],Dist[30001];
int Distanta[30001],Coada[30001],noduri,muchi,start,fin,i,x,y,d;
bool Vizitat[30001];
int main()
{
std::ios::sync_with_stdio(false);
// freopen("sate.in","r",stdin);
f>>noduri>>muchi>>start>>fin;
//scanf("%i %i %i %i",&noduri,&muchi,&start,&fin);
for (i=0;i<muchi;i++)
{
f>>x>>y>>d;
//scanf("%i %i %i",&x,&y,&d);
Nod[x].push_back(y);
Dist[x].push_back(d);
Nod[y].push_back(x);
Dist[y].push_back(d);
}
Coada[0]=start;
int k=0;
int q=0;
while (k<=q)
{
for (i=0;i<Nod[Coada[k]].size()&&k<=q;i++)
{
if (Nod[Coada[k]][i]==fin)
{
if (Coada[k]>Nod[Coada[k]][i])
Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]-Dist[Coada[k]][i];
else
Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]+Dist[Coada[k]][i];
g<<Distanta[Nod[Coada[k]][i]];
k=q+10;
return 0;
}
else if (Vizitat[Nod[Coada[k]][i]]==false)
{
q++;
Vizitat[Nod[Coada[k]][i]]=true;
Coada[q]=Nod[Coada[k]][i];
if (Coada[k]>Nod[Coada[k]][i])
Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]-Dist[Coada[k]][i];
else
Distanta[Nod[Coada[k]][i]]=Distanta[Coada[k]]+Dist[Coada[k]][i];
}
}
k++;
}
}