#include <bits/stdc++.h>
#define int long long
using namespace std;

vector<pair<int,int>>M[30001];
int dist[30001];
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<>>q;
int n,m;
int x,y;
void dijk(int nod)
  {
       for(int i = 1;i<=n;++i)
          dist[i] = 1e14;

          dist[nod] = 0;

         q.push({dist[nod],nod});
      while(!q.empty())
    {
        int x = q.top().second;
        q.pop();
        for(auto i : M[x])
        {
            int vec = i.first;
            int cost = i.second;
            if(dist[vec] > dist[x] + cost)
            {
                dist[vec]= dist[x] + cost;
                q.push({dist[vec],vec});

            }
        }
    }


  }



signed main() {

freopen ("sate.in","r",stdin);
freopen ("sate.out","w",stdout);
   cin >> n >> m >> x >> y;
   for(int i = 1;i<=m;++i)
    {
        int st,dr,c;
        cin >> st >> dr >> c;
        M[st].push_back({dr,c});
        M[dr].push_back({st,-c});


    }
   dijk(x);
   cout << dist[y];









    return 0;
}