#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream cin("sate.in");
ofstream cout("sate.out");
int n,m;
int start,final;
int x,y;
long long c;
vector<vector<pair<int,int> > > A;
vector<bool> fr;
void bfs()
{
    queue<pair<int,long long> > Q;
    Q.push({start,0});
    fr[start]=1;
    while(!Q.empty())
    {
       int cap=Q.front().first;
       int cost=Q.front().second;
       Q.pop();
       if(cap==final)
       {
           cout<<cost;
           exit(0);
       }
       for(int i=0;i<A[cap].size();i++)
       {
           int vecin=A[cap][i].first;
           long long new_cost=A[cap][i].second;
           if(!fr[vecin])
           {
               fr[vecin]=1;
               if(cap<vecin)
                  Q.push({vecin,cost+new_cost});
               else
                 Q.push({vecin,cost-new_cost});
           }
       }
    }
}
int main()
{
    cin>>n>>m;
    cin>>start>>final;
    A.resize(n+1);
    fr.resize(n+1);
    for(int i=0;i<m;i++)
    {
        cin>>x>>y>>c;
        A[x].push_back({y,c});
        A[y].push_back({x,c});
    }
    bfs();
    return 0;
}