#include <iostream>
#include <fstream>
#include <set>
#include <vector>


using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");

set <pair <int ,int > > S;
vector < int > V[30001];
vector < int > C[30001];
vector <int > D(300001,1<<30);
void dijkstra(int nod){
    S.insert(make_pair(nod,0));
    while(!S.empty()){
        int nod=(*S.begin()).first;
        int dist=(*S.begin()).second;
        S.erase(S.begin());
        for(int i=0;i<V[nod].size();i++){
            if(D[V[nod][i]]>dist+C[nod][i]){
                D[V[nod][i]]=dist+C[nod][i];
                S.insert(make_pair(V[nod][i],D[V[nod][i]]));
            }
        }
    }
}
int main()
{
    int x,y,c,n,m,xi,yi;
    f>>n>>m>>xi>>yi;
    for(int i=0;i<m;i++){
        f>>x>>y>>c;
        V[x].push_back(y);
        C[x].push_back(c);
        V[y].push_back(x);
        C[y].push_back(-c);
    }

    dijkstra(xi);
    g<<D[yi];
    return 0;
}