#include<bits/stdc++.h>
#define needforspeed ios::sync_with_stdio(0);cin.tie(0)
#define endl '\n'
#define pb push_back
#define mp make_pair
#define mp3(a,b,c) make_pair(a,make_pair(b,c))
#define mp4(a,b,c,d) make_pair(make_pair(a,b),make_pair(c,d))
#define trace1(a) cout << (a) << endl;
#define trace2(a,b) cout << (a)  << " " << (b) << endl;
#define trace3(a,b,c) cout << (a)  << " " << (b) << " " << (c) << endl;
#define trace4(a,b,c) cout << (a)  << " " << (b) << " " << (c) <<  << (d) << endl;
#define ms(a,b) memset( (a), (b), sizeof(a))
#define fi(x) freopen(x,"r",stdin)
#define fo(x) freopen(x,"w",stdout)
#define all(x) (x).begin(),(x).end()
#define len(x) (int)(x).size()
#define xx first
#define yy second
#define LL long long
#define MAXN (int)10005
#define inf 0x3f3f3f3f
#define DB 0
using namespace std;

int N,M;
bool visited[MAXN];
map< pair<int,int>, int>dist;// node,sitance -> occurrences
vector< pair<int,int> >adj[MAXN];// node,distance

void dijkstra(int start,int dest){
     set< pair< pair<int,int>,int > >q;// distance, node, occurrences
     q.insert(mp(mp(0,start),1));
     dist[mp(start,0)] = 1;// node,distance -> occurrence
     ms(visited,false);
     visited[start] = true;
     while(!q.empty()){
         pair< pair<int,int>, int> C = *(q.begin());
         swap(C.xx.xx,C.xx.yy);// swap the distance with the node,  we only had this so that the set would prioritize by distance
         C.yy = dist[C.xx];// we update it to have the most recent occurrrence count
         // C = (node,distance,occurrences)
         q.erase(q.begin());
         if(C.xx.xx == dest)return;
         if(DB)trace3(C.xx.xx,C.xx.yy,C.yy);
         for(pair<int,int>&E : adj[C.xx.xx]){
             pair< pair<int,int>,int >NEXT = mp(mp(E.xx,E.yy+C.xx.yy),C.yy);
             if(DB){
               cout << "EDGE ";
               trace3(NEXT.xx.xx,NEXT.xx.yy,NEXT.yy);
             }
             if(dist.count(NEXT.xx))
                dist[NEXT.xx]+=NEXT.yy;
             else{
                if(!visited[NEXT.xx.xx]){// the node hasn't been visited
                   if(DB)cout << "VISITED" << endl;
                   visited[NEXT.xx.xx] = true;
                   dist[NEXT.xx] = NEXT.yy;
                   swap(NEXT.xx.xx,NEXT.xx.yy);
                   q.insert(NEXT);
                }
                else{// the node has been visisted so we want to limit what we push
                    pair< pair<int,int>,int> D = *(--dist.upper_bound(NEXT.xx));
                    if(DB){
                      cout << "VISITED" << endl;
                      trace3(D.xx.xx,D.xx.yy,D.yy);
                    }
                    if(D.xx.yy > NEXT.xx.xx){
                      visited[NEXT.xx.xx] = true;
                      dist[NEXT.xx] = NEXT.yy;
                      swap(NEXT.xx.xx,NEXT.xx.yy);// swap them so it becomes (distance,node,occurrences) again
                      q.insert(NEXT);
                    }
                }
             }
         }


     }

}

int main() {
  #ifdef DBa
  fi("input.txt");
  #endif
  needforspeed;
  cin >> N >> M;
  for(int i = 0;i < M;i++){
      int u,v,w;
      cin >> u >> v >> w;
      adj[u].pb(mp(v,w));
  }
  int s,t;
  cin >> s >> t;
  dijkstra(s,t);
  if(visited[t]){
     pair< pair<int,int>,int> OUT = *(dist.upper_bound(mp(t,-1)));
     cout << OUT.yy << endl;
  }
  else
      cout << -1 << endl;
  return 0;
}