#include<iostream>

 #include<queue>

 using namespace std;

 queue<int>q;

 struct Edge{

     int pre,to,w;

 }edge[];

 int head[];

 bool if_q[];

 int dis[];

 int T, C, Ts, Te,Rs, Re,Ci;

 int num_edge;

 inline void add_edge(int from,int to,int w)

 {

     edge[++num_edge].pre=head[from];

     edge[num_edge].to=to;

     edge[num_edge].w=w;

     head[from]=num_edge;

 }

 inline void spfa(int u)

 {

      q.push(u);

      if_q[u]=true;

      while(!q.empty())

      {

          u=q.front();

          for(int i=head[u]; i!=; i=edge[i].pre)

          {

              int v=edge[i].to;

              if(dis[u]+edge[i].w<dis[v])

              {

                  dis[v]=dis[u]+edge[i].w;

                  if_q[v]=true;

                  q.push(v);

              }

          }

          if_q[u]=false;

          q.pop();

       }

 }

 int main()

 {

     for(int i=;i<;i++)

         dis[i]=0x7fffffff;

     cin>>T>>C>>Ts>>Te;

     for(int i=;i<C;i++)

     {

         cin>>Rs>>Re>>Ci;

         add_edge(Rs,Re,Ci);

         add_edge(Re,Rs,Ci);

     }

     dis[Ts]=;

     spfa(Ts);

     cout<<dis[Te];

     return ;

 }