1 #include<iostream>
 2 #include<cstdio>
 3 #include<queue>
 4 #include<cstring>
 5 using namespace std;
 6 const int maxn1=2505;
 7 const int maxn2=6205;
 8 const int INF=0x3f3f3f3f;
 9 int dist[maxn1],head[maxn1];
10 bool vis[maxn1];
11 int a,b,c,d;
12 struct pot{
13     int id;
14     int goal;
15     bool operator <(const struct pot & AA)const
16     {
17         return goal > AA.goal;
18     }
19 };
20 struct edge{
21     int to;
22     int next;
23     int len;
24     
25 }EDGE[maxn2*2];
26 int edge_cnt=0;
27 priority_queue<struct pot>pq;
28 void add(int x,int y,int z)
29 {
30     EDGE[edge_cnt].to=y;
31     EDGE[edge_cnt].len=z;
32     EDGE[edge_cnt].next=head[x];
33     head[x]=edge_cnt++;
34 }
35 void dij()
36 {
37     while(!pq.empty())pq.pop();
38     pq.push((struct pot){c,0});
39     while(!pq.empty())
40     {
41         struct pot qwq=pq.top();pq.pop();
42         if(dist[qwq.id]<qwq.goal)
43         continue;
44         if(qwq.id==d)break;
45         vis[qwq.id]=1;
46         for(int i = head[qwq.id];i!=-1;i=EDGE[i].next)
47         {
48             int v=EDGE[i].to;
49             if(qwq.goal+EDGE[i].len<dist[v]&&!vis[v])
50             {
51                 dist[v]=qwq.goal+EDGE[i].len;
52                 pq.push((struct pot){v,dist[v]});
53             }
54         }
55     }
56     
57 }
58 int main()
59 {
60     scanf("%d%d%d%d",&a,&b,&c,&d);
61     for(int i = 1 ; i <= a ; i++)
62     {
63         dist[i]=INF;
64     }
65     dist[c]=0;
66     memset(head,-1,sizeof(head));
67     memset(vis,0,sizeof(vis));
68     while(b--)
69     {
70         int q,w,e;
71         scanf("%d%d%d",&q,&w,&e);
72         add(q,w,e);
73         add(w,q,e);
74     }
75     dij();
76     printf("%d\n",dist[d]);
77     
78     return 0;
79 }