using namespace std;

#include<iostream>
#include<fstream>
#include<vector>
#include<queue>
#define pb push_back
#define nmax 30010
#define oo 0x3f3f3f3f
struct nod{
int lg,c;};
vector<nod> G[nmax];
queue<int> q;
int N,M,X,Y;
int isinq[nmax],dp[nmax];
ofstream fout("sate.out");
void solve()
{int u;
vector<nod>::iterator it;
int i;
q.push(X);
isinq[X]=1;
for(i=1;i<=N;i++)
  dp[i]=oo;
dp[X]=0;
  while(!q.empty())
  {
      u=q.front();
      q.pop();
      isinq[u]=0;
      for(it=G[u].begin();it<G[u].end();it++)
      {
          if(dp[it->lg]>dp[u]+it->c)
          {
              dp[it->lg]=dp[u]+it->c;
              if(!isinq[it->lg])
              {
                  q.push(it->lg);
                  isinq[it->lg]=1;
              }
          }
      }
  }
    fout<<dp[Y]<<"\n";

}

void cit()
{
    ifstream fin("sate.in");
    int i,x,y,z;
    fin>>N>>M>>X>>Y;
    for(i=1;i<=M;i++)
    {
        fin>>x>>y>>z;
        G[x].pb((nod){y,z});
        G[y].pb((nod){x,-z});
    }

    fin.close();
}

int main()
{

    cit();

    solve();

    fout.close();

    return 0;
}