#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=0,b=0,c;
    in>>n>>m>>st>>fin;
    char ch;
    in.get(ch);
    while (m--)
    {
      a=b=c=0;
      int cntspatiu=0;
      while (in.get(ch)&&ch!='\n')
      {
        if (ch<='9'&&ch>='0')
        {
          if (cntspatiu==0)
            a=a*10+ch-'0';
          else if (cntspatiu==1)
            b=b*10+ch-'0';
          else
            c=c*10+ch-'0';
        }
        else
          cntspatiu++;
      }
      v[a].push_back({b,c});
      v[b].push_back({a,c});
    }
    drum (st,0);
    return 0;
}