#include <bits/stdc++.h>

using namespace std;
ifstream fin("sate.in");
ofstream fout("sate.out");
vector <pair<int,int>>v[300001];
bool ver[300001];
int x,y,sol=0;
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>Q;
void bfs(int c,int i)
{
    Q.pop();
    ver[i]=true;
    if(i==y)
    {
        sol=c;
        return;
    }
    for(auto y:v[i])
    {
        if(ver[y.second]==false)
        {
            Q.push(make_pair(c+y.first,y.second));
        }
    }
}
int main()
{
  int i,n,m,x1,x2,c;
  fin>>n>>m>>x>>y;
  for(i=1;i<=m;i++)
  {
      fin>>x1>>x2>>c;
      v[x1].push_back(make_pair(c,x2));
      v[x2].push_back(make_pair(-c,x1));
  }
  if(x>y)swap(x,y);
  Q.push(make_pair(0,x));
  while(ver[y]==false)
  {
      if(ver[Q.top().second]==false)
      {
      bfs(Q.top().first,Q.top().second);
      }
  }
  fout<<sol;
}