#include <bits/stdc++.h>

#define pb push_back
#define int ll
using namespace std;
ifstream f ( "sate.in" );
ofstream g ( "sate.out");

vector < pair <int ,int > > v[30005];
bool viz[30005];
int n,m,x,y,ans;

void parcg (int nod)
{
    if(nod==y) return;
    viz[nod]=1;
    for(int i=0;i<v[nod].size();i++)
    {
        int vecin=v[nod][i].first;
        int cost= v[nod][i].second;
        if(!viz[vecin])
        {   viz[vecin]=1;
            if(vecin<nod) ans-=cost;
            else ans+=cost;
            parcg(vecin);
        }
    }

}

main()
{
    f>>n>>m>>x>>y;

    for(int i=1;i<=m;i++)
    {
        int a,b,x;
        f>>a>>b>>x;
        v[a].pb({b,x});
        v[b].pb({a,x});
    }
    parcg(x);
    g<<ans;
    return 0;
}