#include <fstream>
#include <vector>
#include <queue>
#define inf 2000000000
using namespace std;

vector <pair<int,pair<int,int> > > g[30005];
int n,m,x,y;


void read()
{
  ifstream d("sate.in");
  int i,j,c;
  d>>n>>m>>x>>y;
  for (int k=1;k<=m;k++)
  {
    d>>i>>j>>c;
    g[i].push_back(make_pair(c,make_pair(i,j)));
    g[j].push_back(make_pair(-c,make_pair(j,i)));
  }
}

int getDist()
{
  int d[30005];
  for (int i=1;i<=n;i++) d[i]=inf;
  d[x]=0;
  queue <int> q;
  q.push(x);
  while (d[y]==inf)
  {
    int e=q.front();
    q.pop();
    vector <pair<int,pair<int,int> > >::iterator it;
    for (it=g[e].begin();it!=g[e].end();it++)
    {
      if(d[(*it).second.second]==inf)
      {
        d[(*it).second.second]=d[(*it).second.first]+(*it).first;
        q.push((*it).second.second);
      }
    }
  }
  return d[y];
}

void write()
{
  ofstream o("sate.out");
  o<<getDist();
}

int main()
{
  read();
  write();
}