#include <fstream>
#include <vector>

using namespace std;

vector < pair <int,int> > v[30001];
bool viz[30001];
int fin;

ifstream in ("sate.in");
ofstream out ("sate.out");

void drum(int nod,int dist)
{
  viz[nod]=1;
  if (nod==fin)
  {
    out<<dist;
  }
  else
  {
    int nod1,d;
    for (int i=0;i<v[nod].size();i++)
    {
      nod1=v[nod][i].first;
      d=v[nod][i].second;
      if (viz[nod1]==0&&nod1<nod)
        drum(nod1,dist-d);
      else if (viz[nod1]==0&&nod1>nod)
        drum(nod1,dist+d);
    }
  }
}

int main()
{
    int n,m,st,a,b,c;
    in>>n>>m>>st>>fin;
    for (int i=1;i<=m;i++)
    {
      in>>a>>b>>c;
      v[a].push_back({b,c});
      v[b].push_back({a,c});
    }
    drum (st,0);
    return 0;
}