#include<fstream>
#include<vector>
#include<queue>
using namespace std;
ifstream f("sate.in");
ofstream g("sate.out");
int n,m,x,y,sol,i;
struct nod{
    int sat,d;
};
vector <nod> v[30003];bool viz[30003];
nod make_nod(int a,int b)
{
    nod c;
    c.sat=a;
    c.d=b;
    return c;
}
void citire()
{
    int a,b,dist;
    f>>n>>m>>x>>y;
    for(int i=1;i<=m;i++)
        {
            f>>a>>b>>dist;
            v[a].push_back(make_nod(b,dist));
            v[b].push_back(make_nod(a,dist));
        }
}

void bfs()
{
    nod p;
    int i;

    queue <nod> q;
    q.push(make_nod(x,0));
    viz[x]=1;
    while(!q.empty() && !viz[y])
    {
        nod t;
        t=q.front();
        q.pop();
        for(i=0;i<v[t.sat].size();i++)
            {
                p=v[t.sat][i];
                if(viz[p.sat]==0)
                    {
                        if(p.sat>t.sat)
                            p.d+=t.d;
                        else
                            p.d=t.d-p.d;
                        viz[p.sat]=1;
                        q.push(p);
                        if(p.sat==y)
                            sol=p.d;
                    }
            }
    }

}
int main()
{
    citire();
    bfs();
    g<<sol;
}