#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream cin("sate.in");
ofstream cout("sate.out");
int n,m;
int start,final;
int a,b,c;
struct pereche{
    int vecin;
    int drum;
};
vector<vector<pereche>> A;
vector<bool> fr;
void bfs()
{
    queue<pair<int,int>> 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].vecin;
            int drum=A[cap][i].drum;
            if(!fr[vecin])
            {
                fr[vecin]=1;
                Q.push({vecin,drum+cost});
            }
        }
    }
}
int main()
{
    cin>>n>>m;
    A.resize(n+1);
    fr.resize(n+1);
    cin>>start>>final;
    for(int i=0;i<m;i++)
    {
        cin>>a>>b>>c;
        if(a>b)
          swap(a,b);
        A[a].push_back({b,c});
        A[b].push_back({a,-c});
    }
    bfs();
    return 0;
}