#include <bits/stdc++.h>

using namespace std;
ifstream fin ("sate.in");
ofstream fout ("sate.out");
const int NMAX=3*1e4+5;
int n,m,x,y,suma;
vector< pair<int,int> > G[NMAX];
bool viz[NMAX];
queue <int> q;
void citire()
{
    fin>>n>>m>>x>>y;
    while(m--)
    {
        int a,b,c;
        fin>>a>>b>>c;
        G[a].push_back({b,c});
        G[b].push_back({a,c});
    }
}
void bfs()
{
    int start=x;
    q.push(x);
    int found=0;
    while(!q.empty() && !found)
    {
        int nods=q.front();
        q.pop();
        for(int i=0;i<G[nods].size();i++)
        {
             if(!viz[G[nods][i].first] && G[nods][i].first!=start)
            {
                if(nods<G[nods][i].first) suma+=G[nods][i].second;
                else                suma-=G[nods][i].second;
                q.push(G[nods][i].first);
                viz[G[nods][i].first]=true;
            }
             if(G[nods][i].first==y) {found=true;break;}

        }
    }
}
int main()
{
    citire();
    bfs();
    fout<<suma;
    return 0;
}